The concept of microbial functional genes has added a new dimension to microbial ecology research by improving the model of microbial community-ecosystem functions relationship. However, our ...knowledge vis-à-vis fine-scale spatial distribution pattern of functional genes and their probable impact on plant community in the hyper-diverse tropical forest ecosystem is very limited. Here, we investigated the spatial pattern of functional genes abundance (NirK, AOA, AOB, and PhoD), identified key influencing factors, and distinguished the key functional group supporting the plant community in a tropical rainforest located in Xishuangbanna. In total, 200 soil samples and vegetation data of ~4800 individuals of plants across a 1 ha study area were collected. Our results detected higher spatial variability with a maximum magnitude of abundance for PhoD gene (4.53 × 107 copies) followed by NirK (2.71 × 106 copies), AOA (1.97 × 106 copies), and AOB (7.38 × 104 copies). A strong spatial dependence was observed for PhoD and NirK over the distance of 17 and 18 m, respectively. Interestingly, the N:P stoichiometry played a critical role in structuring the spatial pattern of the most abundant PhoD gene. The significant positive and negative relationship of PhoD with N:P ratio and available phosphorus, respectively, indicated that the P-limiting environment was a driving factor for recruitment of PhoD gene community. The structural equation modeling ascertained the direct positive impact of PhoD on plant biomass and high demand of available P by plants suggesting that the organic phosphorus mineralization process is essential to maintain plant productivity by re-establishing the availability of the most limiting P nutrient. Our preliminary study improves our understanding of how microbial functional genes-environment associations could be used for monitoring soil health and its overall impact on ecosystem multifunctionality. Finally, we intend to conduct the study at a large spatial scale for achieving a holistic view.
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•Spatial pattern of microbial functional genes was investigated in tropical forest.•PhoD gene abundance was higher than Nirk, AOA, and AOB.•PhoD gene abundance was positively correlated with soil N:P ratio.•Only PhoD gene showed a direct positive impact on the plant biomass.•Nutrient stoichiometry and plant community drive the spatial variability.
To understand soil biodiversity we need to know how soil communities are assembled. However, the relationship between soil community assembly and environmental factors, and the linkages between soil ...microbiota taxonomic groups and their body sizes, remain unexplored in tropical seasonal rainforests. Systematic and stratified random sampling was used to collect 243 soil and organism samples across a 20‐ha plot in a tropical seasonal rainforest in southwestern China. High‐throughput sequencing, variation analysis and principal coordinates of neighbourhood matrices were performed. Soil community composition, spatial distribution and assembly processes based on propagule size (including archaea, bacteria, fungi and nematodes) were investigated. The results showed that: (i) the community assembly of small soil microorganisms (bacteria, fungi) was mostly influenced by stochastic processes while that of larger soil organisms (nematodes) was more deterministic; (ii) the independent effects of habitat (including soil and topographic variables) and its interaction with plant attributes for community structure significantly decreased with increasing body size; and (iii) plant leaf phosphorus directly influenced the spatial distribution of soil‐available phosphorus, which indicates their indirect impact on the assembly of the soil communities. Our data suggest that the assembly of multitrophic soil communities can be explained to some extent by changes in above‐ground plant attributes. This highlights the importance of above‐ and below‐ground linkages in influencing multitrophic soil microbiota community assembly.
Plants allocate biomass to different organs in response to resource variation for maximizing performance, yet we lack a framework that adequately integrates plant responses to the simultaneous ...variation in above‐ and below‐ground resources. Although traditionally, the optimal partition theory (OPT) has explained patterns of biomass allocation in response to a single limiting resource, it is well‐known that in natural communities multiple resources limit growth. We study trade‐offs involved in plant biomass allocation patterns and their effects on plant growth under variable below‐ and above‐ground resources—light, soil N and P—for seedling communities.
We collected information on leaf, stem and root mass fractions for more than 1,900 seedlings of 97 species paired with growth data and local‐scale variation in abiotic resources from a tropical forest in China.
We identified two trade‐off axes that define the mass allocation strategies for seedlings—allocation to photosynthetic versus non‐photosynthetic tissues and allocation to roots over stems—that responded to the variation in soil P and N and light. Yet, the allocation patterns did not always follow predictions of OPT in which plants should allocate biomass to the organ that acquires the most limiting resource. Limited soil N resulted in high allocation to leaves at the expense of non‐photosynthetic tissues, while the opposite trend was found in response to limited soil P. Also, co‐limitation in above‐ and below‐ground resources (light and soil P) led to mass allocation to stems at the expense of roots. Finally, we found that growth increased under high‐light availability and soil P for seedlings that invested more in photosynthetic over non‐photosynthetic tissues or/and that allocated mass to roots at the expense of stem.
Synthesis. Biomass allocation patterns to above‐ and below‐ground tissues are described by two independent trade‐offs that allow plants to have divergent allocation strategies (e.g. high root allocation at the expense of stem or high leaf allocation at the expense of allocation to non‐photosynthetic tissues) and enhance growth under different limiting resources. Identifying the trade‐offs driving biomass allocation is important to disentangle plant responses to the simultaneous variation in resources in diverse forest communities.
Biomass allocation patterns to above‐ and below‐ground tissues are described by two independent trade‐offs that allow plants to have divergent allocation strategies (e.g. high root allocation at the expense of stem or high leaf allocation at the expense of allocation to non‐photosynthetic tissues) and enhance growth under different limiting resources. Identifying the trade‐offs driving biomass allocation is important to disentangle plant responses to the simultaneous variation in resources in diverse forest communities
Questions
Trait–environment relationships hold great promise for elucidating the mechanisms that drive community assembly. We asked to what extent does functional trait coordination underlie the ...differentiation of acquisitive–conservative strategies along environmental gradients? Also, to what extent does soil water availability determine trait combinations and subsequently shape microhabitat preferences for species with distinct ecological strategies?
Location
Yunnan Province, southwest China.
Methods
Pearson correlation and trait network analyses were used to quantify trait associations. A combined RLQ–fourth‐corner analysis and a spatial autoregressive error model were employed to examine trait–environment relationships and explain species distribution along environmental gradients.
Results
Leaf and stem traits were tightly coordinated along the first RLQ axis. Herein, traits representing construction cost exhibited trade‐offs against traits representing resource acquisition rate, underlying an acquisitive–conservative strategy differentiation along the environmental gradients. Significant overall and bivariate trait–environment relationships were found. In addition, the topographic wetness index contributed substantially to the environmental variation, and significantly influenced most traits alone. These results supported the hypothesis that soil water availability was the key environmental factor in selecting trait combinations and driving the differentiation of acquisitive and conservative strategies for coexisting species compared with other environmental factors. Finally, deciduous and a proportion of the evergreen species were acquisitive, whereas the remaining evergreen species were conservative, preferring wetter and drier microhabitats, respectively.
Conclusions
Our findings indicate that soil water availability plays a central role in shaping both the trait combinations and microhabitat preferences of species with different ecological strategies rather than different leaf habits. These findings also highlight the fundamental significance of functional traits in facilitating the differentiation between acquisitive and conservative strategies along environmental gradients.
We observed tight trait coordination underlying the differentiation of acquisitive and conservative strategies along environmental gradients in the Ailaoshan subtropical mid‐mountain moist evergreen broad‐leaved forest. In addition, our findings suggest that soil water availability is the primary factor shaping the microhabitat preference of coexisting woody species, mainly through driving the differentiation of diverse ecological strategies.
•Snow damages to canopy increases seedling richness and abundance via recruitment.•Most of the high-recruiting seedlings are light demanding species.•Topographic habitat and spatial pattern also ...affect seedling composition.
We investigated the relative and combined effect of topography and light environment on the recruitment of seedlings in a subtropical forest after snow damage to the canopy. The tree seedling community in an old-growth subtropical forest was monitored using 500 2 m × 2 m seedling plots at six-month intervals for 2 years. With a focus on recruitment following canopy damage, we related abiotic and biotic environmental variables to seedling dynamics, and we tested if significant topographic and light habitat associations were present for seedlings recruiting via a torus translation test. Then, we used variance partitioning to examine the relative effects of spatial, topographic and light variables on the temporal assemblages of seedlings. A total of 3047 seedlings from 58 species recruited in the first 2 years following snow damage. At the community level, increases in seedling abundance and richness were positively correlated with canopy openness and negatively correlated with elevation. At the species level, both pioneer and late-successional tree species had more recruits in high light environment than in low light environment. 84.3% of the recruiting seedlings were significantly associated to either light environment (35.7%), topography (26.5%) or both (22.1%). Despite this, at the plot level, spatial variables (PCNM) explained the majority of the variability in seedling composition over time. Our results suggest that snow damage to the canopy increases species richness and abundance via light-facilitated seedling recruitment, and that the composition of recruiting seedlings was largely spatially dependent. Topographic habitat filtering acts as a persistent force in determining the recruitment of seedlings and increases in strength with increased light-facilitated seedling recruitment. Our results highlight that, in this subtropical forest, both light requirement and topographic specialization interact over time to play a key role in promoting coexistence of tree species through selection of individuals at the seedling stage. We also suggest exploring the possibilities of management intervention to speed up the recovery of this forest.
Tropical forest contributes to > 50% of global litterfall mercury (Hg) inputs and surface soil Hg storage, while with limited understanding of Hg biogeochemical processes. In this study, we displayed ...the 5−m resolution of Hg spatial distribution in three 1-ha tropical forest plots across the latitudinal gradient in Southwest China, and determined Hg isotopic signatures to understand factors driving Hg spatial distribution and sequestration processes. Our results show that tropical forest at the lowest latitude has the highest litterfall Hg input (74.95 versus 34.14−56.59 μg m-2 yr-1 at higher latitude plots), but the smallest surface soil Hg concentration (2−3 times smaller than at higher latitude sites). Hg isotopic evidence indicates that the decreasing climate mediated microbial Hg reduction in forest floor leads to the increasing Hg accumulation along the latitudinal gradient in three tropical forests. The terrain induced indirect effects by influencing litterfall Hg inputs, soil organic matters distribution and interplays between surface and deep soils drive the heterogeneity of surface soil Hg distribution within each sampling plot. Our results highlight though the elevated litterfall Hg inputs, the distinct post-depositional reductions induced Hg loss would remarkedly decrease atmospheric Hg net sink in tropical forest.
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•The increasing surface soil mercury accumulation is observed along latitudinal gradient.•Terrain and climate are main factors to drive the spatial distributions of tropical Hg.•Microbial reduction mainly contributes to tropical Hg loss and isotopic fractionation.•Atmospheric mercury net sink in tropical forests is likely much smaller than in other forests.
Ecologists have historically sought to identify the mechanisms underlying the maintenance of local species diversity. High-dimensional trait-based relationships, such as alternative phenotypes, have ...been hypothesized as important for maintaining species diversity such that phenotypically dissimilar individuals compete less for resources but have similar performance in a given environment. The presence of alternative phenotypes has primarily been investigated at the community level, despite the importance of intraspecific variation to diversity maintenance. The aims of this research are to (1) determine the presence or absence of intraspecific alternative phenotypes in three species of tropical tree seedlings, (2) investigate if these different species use the same alternative phenotypes for growth success, and (3) evaluate how findings align with species co-occurrence patterns. We model species-specific relative growth rate with individual-level measurements of leaf mass per area (LMA) and root mass fraction (RMF), environmental data, and their interactions. We find that two of the three species have intraspecific alternative phenotypes, with individuals within species having different functional forms leading to similar growth. Interestingly, individuals within these species use the same trait combinations, high LMA
×
low RMF and low LMA
×
high RMF, in high soil nutrient environments to acquire resources for higher growth. This similarity among species in intraspecific alternative phenotypes and variables that contribute most to growth may lead to their negative spatial co-occurrence. Overall, we find that multiple traits or interactions between traits and the environment drive species-specific strategies for growth, but that individuals within species leverage this multi-dimensionality in different ways for growth success.
The functional trait values that constitute a whole-plant phenotype interact with the environment to determine demographic rates. Current approaches often fail to explicitly consider trait × trait ...and trait × environment interactions, which may lead to missed information that is valuable for understanding and predicting the drivers of demographic rates and functional diversity. Here, we consider these interactions by modeling growth performance landscapes that span multidimensional trait spaces along environmental gradients. We utilize individual-level leaf, stem, and root trait data combined with growth data from tree seedlings along soil nutrient and light gradients in a hyper-diverse tropical rainforest. We find that multiple trait combinations in phenotypic space (i.e., alternative designs) lead to multiple growth performance peaks that shift along light and soil axes such that no single or set of interacting traits consistently results in peak growth performance. Evidence from these growth performance peaks also generally indicates frequent independence of above- and belowground resource acquisition strategies. These results help explain how functional diversity is maintained in ecological communities and question the practice of utilizing a single trait or environmental variable, in isolation, to predict the growth performance of individual trees.
Understanding tree species responses to biotic and abiotic factors is fundamental for stronger predictions of community assembly and dynamics. However, several challenges remain. These include a ...failure to investigate whether there is evidence for key hypothesized life‐history trade‐offs and to link these trade‐offs to functional traits.
In this study, we seek to explicitly address the above outstanding challenges by constructing models for individual seedling growth in response to abiotic and biotic factors using 3 years of seedling census data from a 20‐ha subtropical forest dynamics plot in a diverse subtropical forest and correlated these responses with functional traits.
We found that light and conspecific neighbours increase and decrease the RGR of tree seedlings respectively. We also found that the ability of a species to positively respond to canopy openness trades‐off against susceptibility to conspecific negative density dependence (CNDD). This trade‐off was evident across seasons and could be predicted on functional trait—stem and leaf dry matter content.
Synthesis. Our findings indicate species that can grow quickly in high‐light environments also tend to suffer more CNDD. The results highlight that strong evidence of a trade‐off relating to growth and defence widely hypothesized to be of importance in diverse tree communities and that this trade‐off occurs across seasons and can be linked to a commonly measured functional trait.
We found tree species that can grow quickly in high light environments also tend to suffer more conspecific negative density dependence. These results highlight strong evidence of a trade‐off relating to growth and defence widely hypothesized to be of importance in diverse tree communities and that this trade‐off occurs across seasons and can be linked to a commonly measured functional trait.
Trait-based approaches have been extensively used in community ecology to provide a mechanistic understanding of the drivers of community assembly. However, a foundational assumption of the trait ...framework, traits relate to performance, has been mainly examined through univariate relationships that simplify the complex phenotypic integration of organisms. We evaluate a conceptual framework in which traits are organized hierarchically combining trait information at the individual- and species-level from biomass allocation and organ-level traits. We focus on photosynthetic traits and predict that the positive effects of increasing plant leaf mass on growth depend on species-level leaf traits. We modeled growth data on more than 1,500 seedlings from 97 seedling species from a tropical forest in China. We found that seedling growth increases with allocation to leaves (high leaf area ratio and leaf mass fraction) and this effect is accentuated for species with high specific leaf area and leaf area. Also, we found that light has a significant effect on growth, and this effect is additive with leaf allocation traits. Our work offers an approach to gain further understanding of the effects of traits on the whole plant-level growth via a hierarchical framework including organ-level and biomass allocation traits at species and individual levels.
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