Forest disturbances at gap levels are one of the most important events for the regeneration and establishment of intermediate tree species. Abrupt canopy openings expose plants to high light ...intensity and high evaporative demands that stress shade-acclimated plants. Later, the slow closure of gaps reduces light availability to plants established when the incident irradiation was higher. This work evaluated the morphological and physiological acclimation of
Cabralea canjerana
(Vell) Mart. regeneration to sudden and to gradual changes in canopy cover. A pot experiment was carried out with plants exposed to a sudden opening. A few days after the light shock, plants rapidly increased photosynthetic rates and decreased leaf water potential. After two months, plants activated physiological responses at leaf and whole plant levels to high light and water stresses, e.g., increased stomatal conductance, stomatal index and reduction of leaf: fine roots ratio and chlorophyll. After seven months, hydraulic conductivity of petioles and the whole leaf increased, and growth was much higher than plants that remained under the canopy. In a field experiment in gaps in the rainforest, plants acclimated to all canopy covers. Seven years after planting, growth was maximum in open environments within the gaps, even if the canopy closed during the first 20 months after planting. In conclusion, if this species is planted to enrich the rainforest, positions within gaps with lower canopy cover should be chosen and gap closure will not affect growth. To manage
C. canjerana
natural regeneration, the opening of gaps and removal of understory will increase survival and growth without the risk that the stress caused by these sudden openings could lead to the death of seedlings. Combining pot and field experiments helps to understand the autecology of trees with particular ecological interest, and to build sound restoration practices.
The stoichiometry of carbon, nitrogen, and phosphorus (C:N:P) among leaves, stems, and roots reflects trade-offs in plants for acquiring resources and their growth strategy. The widely distributed ...plant
Alhagi sparsifolia
is an ideal species to study the ecological stoichiometry in different organs in response to the availability of nutrients and water in the desert ecosystem. However, which response of organs is most sensitive to environmental conditions is still unclear. To answer this question, we collected samples of plants and soils including not only aboveground leaves and stems, but also underground roots and soils from a wide range of arid areas during the growing season. The C, N, P, C:N, C:P, and N:P ratios in leaves, thorns, stems, and roots were derived to explore their relationship as well as their response mechanisms to nutrients and water spanning 1 m deep in the soil. The results showed that the order of N concentration was leaves > thorns > stems > roots, that the concentration of P in the leaves, thorns, and stems was similar, and that their values were higher than those in the roots. First, the C:N ratios in the leaves and stems were significantly positively correlated with the ratio in roots. The C:N ratios in each organ showed a significant relationship with the soil alkali hydrolyzable nitrogen (SAN) above a depth of 60 cm. In addition to SAN, soil available phosphorus (SAP) and soil organic carbon (SOC) affect the C:N ratio in the roots. Second, the C:P and N:P ratios in aboveground organs showed no correlations with the ratios in roots. The C:P and N:P ratios in the leaves and thorns have no relationship with soil nutrients, while the C:P ratio in roots was influenced by SAN and SOC in all soil layers. Finally, the N:P ratios in roots were also affected by nutrients in different soil depths at 0–20 and 60–80 cm. These results illustrate that the roots were more sensitive to soil nutrients than the aboveground parts. Our study of ecological stoichiometry also suggests a novel systematic approach for analyzing the sensitivity of responses of an organ to environmental conditions.
(Gold Phoebe) is a threatened tree species in China and a valuable and important source of wood and bioactive compounds used in medicine. Apart from anthropogenic disturbances, several biotic ...constraints currently restrict its growth and development. However, little attention has been given to building adaptive strategies for its conservation by examining its morphological and physio-biochemical responses to drought stress, and the role of fertilizers on these responses. A randomized experimental design was used to investigate the effects of two levels of irrigation (well-watered and drought-stressed) and phosphorous (P) fertilization treatment (with and without P) to assess the morphological and physio-biochemical responses of
seedlings to drought stress. In addition, we evaluated whether P application could mitigate the negative impacts of drought on plant growth and metabolism. Drought stress had a significant negative effect on the growth and metabolic processes of
. Despite this, reduced leaf area, limited stomatal conductance, reduced transpiration rate, increased water use efficiency, enhanced antioxidant enzymes activities, and osmolytes accumulation suggested that the species has good adaptive strategies for tolerating drought stress. Application of P had a significant positive effect on root biomass, signifying its improved water extracting capacity from the soil. Moreover, P fertilization significantly increased leaf relative water content, net photosynthetic rate, and maximal quantum efficiency of PSII under drought stress conditions. This may be attributable to several factors, such as enhanced root biomass, decreased malondialdehyde content, and the up-regulation of chloroplast pigments, osmolytes, and nitrogenous compounds. However, P application had only a slight or negligible effect on the growth and metabolism of well-watered plants. In conclusion,
has a strong capability for drought resistance, while P application facilitates and improves drought tolerance mostly through physio-biochemical adjustments, regardless of water availability. It is imperative to explore the underlying metabolic mechanisms and effects of different levels of P fertilization on
under drought conditions in order to design appropriate conservation and management strategies for this species, which is at risk of extinction.
Intercropping is an important practice in promoting plant diversity and productivity. Compared to the accumulated understanding of the legume/non-legume crop intercrops, very little is known about ...the effect of this practice when applied to native species on soil microbial communities in the desert ecosystem. Therefore, in the present study, bulk soil and rhizosphere microbial communities in the 2-year
Alhagi sparsifolia
(legume)/
Karelinia caspica
(non-legume) monoculture vs. intercropping systems were characterized under field conditions. Our result revealed that plant species identities caused a significant effect on microbial community composition in monocultures but not in intercropping systems. Monoculture weakened the rhizosphere effect on fungal richness. The composition of bacterial and fungal communities (β-diversity) was significantly modified by intercropping, while bacterial richness (Chao1) was comparable between the two planting patterns. Network analysis revealed that Actinobacteria, α- and γ-proteobacteria dominated bulk soil and rhizosphere microbial co-occurrence networks in each planting pattern. Intercropping systems induced a more complex rhizosphere microbial community and a more modular and stable bulk soil microbial network. Keystone taxa prevailed in intercropping systems and were Actinobacteria-dominated. Overall, planting patterns and soil compartments, not plant identities, differentiated root-associated microbiomes. Intercropping can modify the co-occurrence patterns of bulk soil and rhizosphere microorganisms in desert ecosystems. These findings provided a potential strategy for us to manipulate desert soil microbial communities and optimize desert species allocation in vegetation sustainability.
Eucalyptus grandis is a globally important tree crop. Greenhouse-grown tree seedlings often face water deficit after outplanting to the field, which can affect their survival and establishment ...severely. This can be alleviated by the application of superabsorbent hydrophilic polymers (SAPs). Growth promoting bacteria can also improve crop abiotic stress tolerance; however, their use in trees is limited, partly due to difficulties in the application and viability loss. In this work, we evaluated the improvement of drought tolerance of E. grandis seedlings by inoculating with two Pseudomonas strains (named M25 and N33), carried by an acrylic-hydrocellulosic SAP. We observed significant bacterial survival in the seedling rhizosphere 50 days after inoculation. Under gradual water deficit conditions, we observed a considerable increase in the water content and wall elasticity of M25-inoculated plants and a trend towards growth promotion with both bacteria. Under rapid water deficit conditions, which caused partial defoliation, both strains significantly enhanced the formation of new leaves, while inoculation with M25 reduced the transpiration rate. Co-inoculation with M25 and N33 substantially increased growth and photosynthetic capacity. We conclude that the selected bacteria can benefit E. grandis early growth and can be easily inoculated at transplant by using an acrylic-hydrocellulosic SAP.
Alhagi sparsifolia (Camelthorn) is a leguminous shrub species that dominates the Taklimakan desert's salty, hyperarid, and infertile landscapes in northwest China. Although this plant can colonize ...and spread in very saline soils, how it adapts to saline stress in the seedling stage remains unclear so a pot-based experiment was carried out to evaluate the effects of four different saline stress levels (0, 50, 150, and 300 mM) on the morphological and physio-biochemical responses in A. sparsifolia seedlings. Our results revealed that N-fixing A. sparsifolia has a variety of physio-biochemical anti-saline stress acclimations, including osmotic adjustments, enzymatic mechanisms, and the allocation of metabolic resources. Shoot-root growth and chlorophyll pigments significantly decreased under intermediate and high saline stress. Additionally, increasing levels of saline stress significantly increased Na.sup.+ but decreased K.sup.+ concentrations in roots and leaves, resulting in a decreased K.sup.+/Na.sup.+ ratio and leaves accumulated more Na + and K + ions than roots, highlighting their ability to increase cellular osmolarity, favouring water fluxes from soil to leaves. Salt-induced higher lipid peroxidation significantly triggered antioxidant enzymes, both for mass-scavenging (catalase) and cytosolic fine-regulation (superoxide dismutase and peroxidase) of H.sub.2O.sub.2. Nitrate reductase and glutamine synthetase/glutamate synthase also increased at low and intermediate saline stress levels but decreased under higher stress levels. Soluble proteins and proline rose at all salt levels, whereas soluble sugars increased only at low and medium stress. The results show that when under low-to-intermediate saline stress, seedlings invest more energy in osmotic adjustments but shift their investment towards antioxidant defense mechanisms under high levels of saline stress. Overall, our results suggest that A. sparsifolia seedlings tolerate low, intermediate, and high salt stress by promoting high antioxidant mechanisms, osmolytes accumulations, and the maintenance of mineral N assimilation. However, a gradual decline in growth with increasing salt levels could be attributed to the diversion of energy from growth to maintain salinity homeostasis and anti-stress oxidative mechanisms.
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•Alhagi sparsifolia offers a variety of socio-ecological services in arid lands.•Unsustainable activities for agricultural purposes may threaten nutrient cycling.•Long-term burning ...and cutting affect the foliar nutrition of A. sparsifolia.•Long-term overexploitation can impact the nutritional quality of A. sparsifolia.•Sustainable management of A. sparsifolia is crucial for ecological restoration.
Arid ecosystems are characterized by low availability and mobility of soil nutrients and slow geochemical cycles. Management of native vegetation in such ecosystems for fuel, livestock grazing, and other agricultural activities (burning and cutting) may threaten semi-natural communities due to the changes in nutrient cycles and soil fertility. Alhagi sparsifolia is a dominant perennial legume in the Taklamakan Desert of northwestern China and has been used as fodder for livestock and plays a crucial ecological role in stabilizing dunes in the oasis-desert ecotone. We evaluated the effects of long-term (12 years) burning and cutting of plant biomass on the mineral nutrition of A. sparsifolia and associated soils at two depths (0–50 and 50–100 cm) in the field conditions following the block design experiment. We found that burning effects tended to be restricted to the topsoil (0–50 cm), and the concentration of many micro-and macronutrients was increased. Burning was associated with a decrease in plant nitrogen (N) and phosphorus (P) concentration, whereas concentrations of other micro-and macronutrients increased; overall, burning reduced foliar stocks of N, P, and potassium (K). Annual cutting elicited smaller increases in soil mineral (total sulfur, total P, calcium, magnesium, and available P and K) concentrations than burning, and soil enzymatic activities increased. There were contrasting response patterns of leaf N and P concentration and macro-and micronutrients between the two management approaches. Burning and cutting reduced leaf N and P concentrations, while changes in root and shoot N and P concentrations depended on treatments. Thus, burning and cutting of A. sparsifolia impact organ nutrient stoichiometry (increased losses of macronutrients from arid plant-soil ecosystems) and nutritional quality (for feeding livestock), particularly due to predicted rises in extreme climatic events under climate change that are expected to increase risks of soil erosion, however, impacts on native trophic webs remain unclear.
Poplar productivity is negatively affected by excess or deficit of water availability and by insect and pathogens that cause defoliation. Some foliar diseases, like leaf rust, produce defoliation at ...the end of the summer. The interaction between water stress and defoliation is poorly understood. Hence, the aim of this work was to test if defoliation would have a stronger effect on growth, biomass and nutrient accumulation in well-watered plants than in water-stressed plants. The experiment started with 36
Populus deltoides
unrooted cuttings, which grew outdoors in pots throughout a complete growing season. Water stresses (flooding and drought) were imposed from early summer when cuttings were established. Defoliation (50%) was applied at the end of summer when plants were acclimated to water stress. We analyzed photosynthetic parameters in response to water stress and biomass, nitrogen and phosphorus accumulation and partitioning at the end of the first growing season. Artificial defoliation produced similar reduction of plant height and aboveground biomass in the three water conditions; but in well-watered plants caused a strong decrease in belowground accumulation. Defoliation increased nitrogen resorption from leaves before abscission only in plants under drought, but it had no effect in nutrient resorption in well-water and flooded plants. Defoliation decreased nitrogen and phosphorus storage in every water condition. The results are relevant to manage poplars in environments with multiple stresses, because defoliation at the end of the growing season and water stress have relevant impact on plant growth, nutrient storage capacity and on the internal distribution of nutrients.
•Plants respond differently to repeated stress than to a single stress.•Alhagi sparsifolia adapts different strategies to cope with drought stress.•Drought-primed seedlings had a lower oxidative ...status than non-primed.•Stress memory helped A. sparsifolia seedlings to overcome subsequent stress.
Perennial trees are often stressed by drought more than once during their life cycle. Our study exposed three-month-old Alhagisparsifolia, with (drought-primed) or without (nonprimed) prior drought stress to subsequent drought for two months, aiming to reveal whether pre-exposure to drought could enhance seedling resistance to subsequent drought and investigated possible underlying mechanisms. Root biomass, leaf relative water content, chlorophyll a, and carotenoids were significantly higher in drought-primed than nonprimed seedlings. They also had reduced concentrations of malondialdehyde, hydrogen peroxide (H2O2), and superoxide anions (O2•−), indicating relief from oxidative stress. This relief was associated with a coordinated upregulation of enzymes scavenging O2•−and H2O2, particularly superoxide dismutase (SOD) and catalase (CAT), and the maintenance of the ascorbate-glutathione (AsA-GSH) redox pool and enzymatic activities (ascorbate peroxidase, mono- and dehydroascorbate reductase, and glutathione reductase), leading to the better regulation of reactive oxygen species. The failure of nonprimed seedlings to upregulate the SOD, CAT, and AsA-GSH cycles nevertheless made the seedlings susceptible to oxidative stress. The increased levels of strigolactones, jasmonic acid, and abscisic acid in drought-primed seedlings reveal their roles in subsequent stress. They also displayed higher gibberellic acid and indole acetic acid. A principal component analysis showed that the seedlings responded differently to drought if they had previously suffered a drought, mainly due to a higher capacity for pigment protection, oxidative scavenging, osmolytes, and anti-stress hormones. Our study provides insights into the benefits of stress memory induced in seedlings by early drought priming as a strategy for overcoming subsequent stress.
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