Background and aims The survival and coexistence of plants in water-limited environments are related to their ability to coordinate water acquisition and regulation of water loss. To assess the ...coordination among below and aboveground hydraulic traits and the diversity of water-use strategies, we evaluated rooting depth and several leaf hydraulic traits of 15 species in campos rupestres, a seasonally-dry biodiversity hotspot in central Brazil. Methods We assessed the depth of plant water acquisition by excavating roots and analyzing the stable isotope composition of hydrogen (δD) and oxygen (δ18O) in the xylem and soil water. We also measured mid-morning stomatal conductance, leaf-water potential at turgor loss point (ΨTLP) and pre-dawn leaf water potentials (ΨPD) during wet and dry seasons. Results We demonstrated that rooting depth is a good predictor of seasonal variations in stomatal conductance and ΨPD. Shallow-rooted plants had greater variation in stomatal conductance and ΨPD than deep-rooted plants. Woody plants with shallower roots also had lower ΨTLP than deep-rooted plants, revealing higher drought resistance. Conclusion We demonstrate that shallow-rooted species, more exposed to variation in water availability, have mechanisms to confer drought resistance through turgor maintenance. Our results support the theory of hydrological niche segregation and its underlying trade-offs related to drought resistance.
During long‐term ecosystem development and its associated decline in soil phosphorus (P) availability, the abundance of mycorrhizal plant species declines at the expense of non‐mycorrhizal species ...with root specialisations for P‐acquisition, such as massive exudation of carboxylates. Leaf manganese (Mn) concentration has been suggested as a proxy for such a strategy, Mn concentration being higher in non‐mycorrhizal plants that release carboxylates than in mycorrhizal plants. Shifts in nitrogen (N)‐acquisition strategies also occur; nodulation in legumes is expected at low N availability, when sufficient P is available. We investigated whether two congeneric legume species (Bossiaea linophylla and Bossiaea eriocarpa) occurring along two long‐term chronosequences on the south‐western Australian coast and grown in a glasshouse at varying N and P supply exhibited plasticity in nutrient‐acquisition strategies. We hypothesised that the shifts in nutrient limitation and nutrient‐acquisition strategies at the community level would also be found at the species level. Leaf N: P ratios and the responses to nutrient availability suggested that growth of both species exhibited P‐limitation in all treatments, due to the very high leaf N of legumes afforded by symbiotic N‐fixation. Mycorrhizal colonisation was not greater at higher P supply, and root exudation of carboxylates was not stimulated at low P supply; both were unrelated to leaf Mn. However, nodule production declined with increasing N supply. We conclude that intraspecific variation in nutrient‐acquisition and use is low in these species, and that the variation at the community level, observed in previous studies, is likely driven by high‐species turnover.
Understanding the mechanisms that underlie the generation of beta‐diversity remains a challenge in ecology. Underground plant adaptations to environmental gradients have received relatively little ...attention.
We studied plant nutrient‐acquisition strategies and nutrient‐use efficiency at three stages of pedogenesis in infertile soils from campos rupestres and on less infertile soil from cerrado sensu stricto in Brazil. All soils support very high plant diversity with high species turnover between soil types at small spatial scales (metres). We expected that differences in nutrient‐acquisition and ‐use strategies would be associated with this high species turnover. With severely decreasing phosphorus (P) availability, we expected the effectiveness of arbuscular mycorrhizal (AM) symbioses for plant P acquisition to decrease, and reliance on nonmycorrhizal strategies (NM) to increase, while maintaining efficient nutrient use.
Concentrations of total soil P and nitrogen (N) were greater in soils in cerrado than in those from campos rupestres, and the more weathered soils from campos rupestres were severely P and N impoverished. The proportion of the root length colonized by AM fungi was 71% in the soils from the cerrado and <1% in the most P‐impoverished soil type from campos rupestres. Conversely, the proportion of species with nonmycorrhizal P‐acquisition strategies such as rhizosheaths was greater in the most P‐impoverished soils. Leaf P and N were very low and decreased with decreasing soil P and N. Leaf N:P ratios suggest P limitation of plant productivity in the campos rupestres but N‐P colimitation in the cerrado. Photosynthetic rates decreased with increasing P impoverishment, but photosynthetic P‐use efficiency was very high and photosynthetic N‐use efficiency moderately high on all soils. Most species had very high P‐remobilization efficiency during leaf senescence (>70%), but only moderate N‐remobilization efficiency (~50%).
Synthesis. We observed very high P‐use efficiency and moderately high N‐use efficiency in campos rupestres and cerrado species, consistent with plant productivity being more strongly limited by P than by N. Our findings demonstrate that different soil characteristics (nutrient availability and soil texture) select for species differing in nutrient‐acquisition and ‐use strategies (especially below‐ground traits) which is likely key for the very high species turnover at a very small scale between soil types (i.e., beta‐diversity) in campos rupestres and cerrado.
Our findings demonstrate that different soil characteristics (nutrient availability and soil texture, 1‐4) select for species differing in nutrient‐acquisition and ‐use strategies (a, b), which are likely key for the very high species turnover at a very small scale between soil types (i.e., beta‐diversity) in hyperdiverse campos rupestres and cerrado in Central Brazil.
Resumo
Compreender os mecanismos subjacentes à geração de diversidade beta continua sendo um desafio para a ecologia. As adaptações subterrâneas das plantas a gradientes ambientais, como a disponibilidade de nutrientes, têm sido pouco investigadas.
Nós estudamos as estratégias de aquisição e a eficiência no uso de nutrientes de plantas em solos inférteis. Conduzimos a pesquisa em três estágios diferentes de pedogênese em campos rupestres e, em um solo um pouco mais fértil de cerrado,no Brasil. Todos os solos comportam uma alta diversidade de plantas, com uma diferenciação na composição de espécies entre diferentes tipos de solo, em escalas espaciais muito pequenas (metros). Nós esperávamos que diferenças nas estratégias de aquisição e uso de nutrientes estivessem associadas à essa divergência na composição de espécies. Com a redução severa na disponibilidade de fósforo (P) nos solos de campos rupestres, nós esperávamos uma redução da efetividade de simbioses com fungos micorrízicos arbusculares para a obtenção de P; um aumento da dependência de estratégias não‐micorrízicas e, a manutenção da eficiência do uso de nutrientes nos diferentes tipos de solo.
As concentrações totais de P e nitrogênio (N) no solo foram maiores no cerrado do que nos campos rupestres. Os solos mais intemperizados dos campos rupestres foram os mais empobrecidos em N e P. A proporção do comprimento das raízes de plantas colonizadas por fungos micorrízicos arbusculares foi de 71% nas plantas de cerrado e <1% nas plantas dos solos mais pobres em P dos campos rupestres. Por outro lado, a proporção de espécies com estratégias para aquisição de P sem micorrizas, como as bainhas radiculares (rhizosheaths) foi maior nos solos mais pobres em P. As concentrações de P e N foliares foram muito baixas e diminuíram com a redução da disponibilidade de P e N no solo. As razões foliares de N: P sugerem que a produtividade vegetal nos campos rupestres é limitada por P, mas colimitada por P e N no cerrado. As taxas fotossintéticas das plantas foram menores nos solos mais pobres em P, no entanto, a eficiência fotossintética no uso de P foi muito alta e a eficiência fotossintética no uso de N foi moderada em todos os tipos de solo. A maioria das espécies apresentou uma eficiência muito alta na remobilização de P durante a senescência foliar (>70%), mas uma eficiência moderada na remobilização de N (~50%).
Síntese. Nossos resultados demonstram que diferentes atributos do solo (disponibilidade de nutrientes e textura) selecionam espécies com estratégias distintas de aquisição e uso de nutrientes, especialmente as estratégias subterrâneas. Essas estratégias são provavelmente a chave para entender a mudança na composição de espécies na pequena escala espacial (diversidade beta) em campos rupestres e cerrado.
Summary
Plant–soil feedbacks (PSFs) underlying grassland plant richness and productivity are typically coupled with nutrient availability; however, we lack understanding of how restoration measures ...to increase plant diversity might affect PSFs. We examined the roles of sward disturbance, seed addition and land‐use intensity (LUI) on PSFs.
We conducted a disturbance and seed addition experiment in 10 grasslands along a LUI gradient and characterized plant biomass and richness, soil microbial biomass, community composition and enzyme activities.
Greater plant biomass at high LUI was related to a decrease in the fungal to bacterial ratios, indicating highly productive grasslands to be dominated by bacteria. Lower enzyme activity per microbial biomass at high plant species richness indicated a slower carbon (C) cycling. The relative abundance of fungal saprotrophs decreased, while pathogens increased with LUI and disturbance. Both fungal guilds were negatively associated with plant richness, indicating the mechanisms underlying PSFs depended on LUI.
We show that LUI and disturbance affect fungal functional composition, which may feedback on plant species richness by impeding the establishment of pathogen‐sensitive species. Therefore, we highlight the need to integrate LUI including its effects on PSFs when planning for practices that aim to optimize plant diversity and productivity.
Species loss leads to changes in ecosystem function and services, impacting human well‐being. Although biodiversity restoration is pivotal to circumvent this situation, the techniques for restoring ...old‐growth savannas are still limited and the restoration outcomes remain unpredictable. Here, we use a trait‐based approach to understand the functional outcomes of ecological restoration via direct seeding in a Brazilian savanna (cerrado, hereafter neotropical savanna). We compared the functional composition from woody and non‐woody component, total biomass, and biomass allocation of a restored relative to a degraded savanna (abandoned pasture) dominated by exotic grasses and a well‐preserved old‐growth native savanna. We found that the functional composition of restored communities was very similar to those dominated by exotic grasses, both characterized by a greater dominance of species with acquisitive traits, higher above‐ground biomass, and lower investment in root biomass. In contrast, the native vegetation exhibited a dominance of conservative traits and higher investment in belowground rather than aboveground biomass. Even though the acquisitive traits in the restored savanna allow a fast aboveground biomass accumulation and soil cover, the lower belowground biomass investment in the restored savanna may limit its resistance and resilience to droughts and fires. Our findings suggest that restoration efforts in neotropical savanna should focus on fostering the establishment of slow‐growing species to recover the ecosystem properties provided by the high biodiversity in neotropical savannas.
Campos rupestres is an extremely phosphorus (P)‐impoverished rocky ecosystem in Brazil. Velloziaceae is an important plant family in this environment, and some species colonize exposed quartzite ...rock. However, we know virtually nothing about their root development and nutrient acquisition within the rock outcrops and their possible role in rock weathering and landscape formation.
We tested the hypothesis that Velloziaceae dissolve P from the rock, enhancing rock weathering. The study was carried out with two Barbacenia species (Velloziaceae) that colonize quartzite rocks. We assessed the root specializations and exudates, and determined the mineralogical composition of the rocks.
The quartzite rocks contained a low concentration of total P in a matrix composed predominantly of silica. Using transmission electron microscopy, we show root growth perpendicular to the rock‐bedding planes. A micro‐XRF set‐up at the XRF beamline of a synchrotron evidenced root‐associated rock dissolution.
The investigated roots show novel morphological and physiological specializations, coined vellozioid roots, which are highly effective at P acquisition. These carboxylate‐releasing roots function like other specialized roots in nutrient‐depleted soils. The rocks represent a barrier for most species, but due to their chemical and physical actions inside the rocks, vellozioid roots play a pivotal role in rock weathering, contributing to shaping the campos rupestres landscapes.
A plain language summary is available for this article.
Plain Language Summary
The campos rupestres (rocky grassland) comprise an old-growth seasonally dry herbaceous ecosystem on mountaintops in central and eastern Brazil and in disjoint areas with sparse shrubs with high ...plant diversity and endemism. This ecosystem consists of sharp-edged quartzite landforms and rocky hillslopes with boulders, blocks, and sparse soil cover. The slopes in these environments have traditionally been viewed as a product of mechanical rock breakdown controlled by structural and lithological features of rocky hillslopes. In addition to the lithological effects on slope evolution, plant cover plays a pivotal role in the geomorphological process. We explored process–form relationships between plant cover and quartzite rocky hillslopes of campos rupestres, considering the functioning of root traits of rock dwelling endemic species of Velloziaceae. Velloziaceae is an iconic plant family in campos rupestres, and several species colonize quartzite rock with different biogeomorphic effects at different scales. We present a conceptual model of the evolution of quartzite hillslopes based on the arenization process driven by roots expressing a specialized nutrient-acquisition strategy: vellozioid roots. Our results show that at the outcrop scale, roots respond to previous lithological characteristics such as joints and fractures that allow root establishment, followed by the release of large quantities of carboxylates that lead to rock dissolution. The microscopic pattern of bioweathering is associated with enlargement of the quartzite secondary porosity through the formation of root microcracks. Roots that are about 100 μm thick form root mats that surround the grains and produce inter-mineral and intra-mineral porosity systems facilitating percolation of water and organic solutes increasing the weathering. This results in arenization of quartzite by grain-by-grain dissolution and reduces the rock strength, which leads to the formation of quartzite hillslopes, driven by a nutrient-acquisition strategy of vellozioid roots. The described biogeomorphic process determines trajectories of the development of landforms through time, slope-sediment production, slope morphology by the production of boulders and block fields, and sand patches that are reworked by surface runoff along the slope. The hillslopes and landforms that develop in campos rupestres are therefore products of self-reinforcing processes involving nutrient acquisition from bedrock by plants and denudation processes. Also, these positive feedbacks characterize the Velloziaceae species as ecosystem engineers.
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•Slope processes investigated in quartzite landscape of Brazil.•Clefts and joints are important places for biogeomorphic activity.•Root-mediated process led to quartzite dissolution.•Root-mediated biogeomorphic processes increase the hillslope development.
Around 40% of the original Brazilian savanna territory is occupied by pastures dominated by fast‐growing exotic C4 grasses, which impact ecosystem nutrient cycling. The restoration of these areas ...depends on the re‐establishment of soil processes.
We assessed how restoration of abandoned pastures through direct seeding of native species and land‐management practices (burning and ploughing) affect soil nutrient cycling dynamics compared with native savannas. We compared the activity of soil enzymes related to carbon, nitrogen (N) and phosphorus (P) cycling as well as soil microbial biomass and soil chemical properties (pH and the concentration of N, P, potassium K and soil organic matter) among abandoned pastures, native savanna and restored areas.
Abandoned pastures had faster nutrient turnover than native savanna, dominated by slow‐growing native species. This pattern was evident from the overall higher biomass‐specific enzyme activities in abandoned pastures than in native savanna. Compared with native savanna, restored areas had similar levels of soil enzyme activities, but lower microbial biomass and soil organic matter. The low enzyme activity in restored areas was likely related to a reduced soil organic carbon concentration due to practices such as burning and ploughing, rather than the restoration of plant–soil feedback. The lower immobilization of nutrients in microbial biomass and lower retention of nutrients in restored areas, compared with native savanna, is expected to favour the re‐establishment of fast‐growing exotic species.
Synthesis and application. Despite reducing the resprouting and germination of exotic grasses and improving the establishment of native grasses in the short term, restoration practices have major impacts on the soil microbial community and soil fertility. The reduction of soil microbial biomass and organic matter content reduces the immobilization of soil nutrients and is expected to favour a fast nutrient turnover in the ecosystem. This may result in the re‐establishment of exotic grasses in the long term. Future efforts should focus on the recovery of soil organic matter content and the establishment of soil microbial communities similar to native ecosystems after the application of land‐management practices. Therefore, the restoration of abandoned pastures should consider a greater focus on restoring soil carbon and nutrient cycling
Despite reducing the resprouting and germination of exotic grasses and improving the establishment of native grasses in the short term, restoration practices have major impacts on the soil microbial community and soil fertility. The reduction of soil microbial biomass and organic matter content reduces the immobilization of soil nutrients and is expected to favour a fast nutrient turnover in the ecosystem. This may result in the re‐establishment of exotic grasses in the long term. Future efforts should focus on the recovery of soil organic matter content and the establishment of soil microbial communities similar to native ecosystems after the application of land‐management practices. Therefore, the restoration of abandoned pastures should consider a greater focus on restoring soil carbon and nutrient cycling.
Abstract
Experimental evidence shows that grassland plant diversity enhances ecosystem functioning. Yet, the transfer of results from controlled biodiversity experiments to naturally assembled ‘real ...world’ ecosystems remains challenging due to environmental variation
among sites
, confounding biodiversity ecosystem functioning relations in observational studies. To bridge the gap between classical biodiversity‐ecosystem functioning experiments and observational studies of naturally assembled and managed ecosystems, we created regionally replicated,
within‐site
gradients of species richness by seeding across agricultural grasslands differing in land‐use intensity (LUI) and abiotic site conditions.
Within each of 73 grassland sites, we established a full‐factorial experiment with high‐diversity seeding and topsoil disturbance and measured 12 ecosystem functions related to productivity, and carbon and nutrient cycling after 4 years. We then analysed the effects of plant diversity (seeded richness as well as realized richness), functional community composition, land use and abiotic conditions on the ecosystem functions within (local scale) as well as among grassland sites (landscape scale).
Despite the successful creation of a
within‐site
gradient in plant diversity (average increase in species richness in seeding treatments by 10%–35%), we found that only one to two of the 12 ecosystem functions responded to realized species richness, resulting in more closed nitrogen cycles in more diverse plant communities. Similar results were found when analysing the effect of the seeding treatment instead of realized species richness.
Among sites
, ecosystem functioning was mostly driven by environmental conditions and LUI. Also here, the only functions related to plant species richness were those associated with a more closed nitrogen cycle under increased diversity.
The minor effects of species enrichment we found suggest that the functionally‐relevant niche space is largely saturated in naturally assembled grasslands, and that competitive, high‐functioning species are already present.
Synthesis
: While nature conservation and cultural ecosystem services can certainly benefit from plant species enrichment, our study indicates that restoration of plant diversity in naturally assembled communities may deliver only relatively weak increases in ecosystem functioning, such as a more closed nitrogen cycle, within the extensively to moderate intensively managed agricultural grasslands of our study.
Plant growth on harsh substrates (habitat specialization) requires specific traits to cope with stressful conditions.
We tested whether traits related to nutrient acquisition (root colonization by ...fungal symbionts, and plant morphological and physiological specializations), and nutrient use (leaf nitrogen (N) and phosphorus (P) concentrations and N‐ and P‐remobilization efficiency), were related to habitat specialization for 27 species of Velloziaceae growing either in soil or on rocks in extremely P‐impoverished campos rupestres habitats. If habitat specialization were to drive trait sorting, then we expect traits to differ between those substrates.
Both soil and rock‐dwelling species presented a very low proportion of root length colonized by arbuscular mycorrhizal and dark‐septate fungi. However, rhizosheaths were only observed in soil‐dwelling species, and vellozioid roots, a specialization that allows for mining P and dissolving quartzite rock, were mostly found in rock‐dwelling species. We did not observe differences in nutrient‐use traits between rock‐ and soil‐dwelling species.
Root specializations are strongly correlated with microhabitats, and the presence of vellozioid roots seems to mediate bare rock specialization. There is an overall P limitation of plant productivity both on rock and in soil of campos rupestres, which does not drive the sorting of traits related to above‐ground nutrient use and symbiotic P acquisition. Therefore, nutrient impoverishment is indeed a very strong environmental filter in campos rupestres as a whole, but habitat specialization plays an important role in the spatial distribution of Velloziaceae between contrasting substrates.
Translated
Resumo
O crescimento de plantas sobre substratos considerados estressantes (especialização de habitat) requer atributos específicos das plantas.
Nós testamos se os atributos relacionados à aquisição de nutrientes (colonização das raízes por fungos simbióticos, especializações morfológicas e fisiológicas das plantas), e ao uso de nutrientes (concentração foliar de nitrogênio (N) e fósforo (P) e eficiência de remobilização de N e P) estavam relacionados com a especialização de habitat. Nós analisamos os atributos em 27 espécies de Velloziaceae que crescem sobre solo ou rocha em campos rupestres extremamente empobrecidos em P. Se a especialização de habitat fosse responsável pela diferenciação dos atributos, então nós esperaríamos que os atributos diferissem entre esses substratos.
Tanto as espécies que crescem sobre solo, quanto as que crescem sobre rocha apresentaram uma proporção muito pequena da raiz colonizada por micorrizas arbusculares e fungos endofíticos melanizados (“dark septate”). No entanto, somente observamos areia aderida às raízes (“rhizosheaths”) nas plantas que crescem sobre solo. As raízes velozióides, uma especialização que permite a dissolução da rocha e a subsequente aquisição de P, foram observadas principalmente nas espécies crescendo sobre rochas. Nós não observamos diferenças entre os atributos relacionados ao uso de nutrientes entre espécies crescendo sobre os diferentes tipos de substrato.
Especializações radiculares apresentaram forte correlação com o microhabitat, e a presença de raízes velozióides parece mediar a especialização no crescimento sobre a rocha nua. Em campos rupestres, existe uma limitação generalizada do crescimento vegetal pela baixa concentração de P, tanto no solo quanto sobre as rochas, o que não resultou em diferenças nos atributos foliares associados com o uso de N e P. Portanto, a escassez de nutrientes constitui de fato um forte filtro ambiental em campos rupestres como um todo, mas a especialização de habitat tem um papel importante na distribuição de espécies das Velloziaceae em substratos contrastantes.
A free Plain Language Summary can be found within the Supporting Information of this article.
A free Plain Language Summary can be found within the Supporting Information of this article.
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