Diversified land conversion deepens understanding of impacts of rapid rubber plantation expansion on plant diversity in the tropics

Impacts of forest expansion on microbial diversity and community assembly in fragmented mountain ecosystems

Under the influence of global climate change and human activities, forest expansion has become increasingly significant in shaping ecosystems. However, its effects on soil microbial communities remain poorly understood. This study investigates the impacts of forest expansion on soil bacteria, fungi, and protists within mountaintop forest ecosystems. Soil samples were collected from three forest habitats: non-forest expansion mountaintops (NFE-Top), forest expansion mountaintops (FE-Top) and mountain bottoms (FE-Bottom). This study revealed that forest expansion promoted microbial sharing between mountaintop and bottom forests, resulting in greater community similarity between FE-Top and FE-Bottom compared to NFE-Top and FE-Bottom. Notably, forest expansion significantly reduced microbial diversity and altered community composition, particularly within bacterial communities. Microbial network analyses indicated that forest expansion mountaintops were more stable, with higher robustness, and lower vulnerability than non-forest expansion mountaintops. Stochastic assembly processes dominated the microbial communities across all forest habitats, with their relative importance increasing after forest expansion. Furthermore, forest expansion decreased the community-level habitat niche breadth of microbial communities. Distinct environmental factors were the primary indicators of microbial community dissimilarities across different habitats, with TP, pH, and moisture acting as key indicators of these differences in NFE-Top, FE-Top, and FE-Bottom, respectively. These findings highlight the important role of forest expansion in shaping microbial community dynamics and emphasize the potential of microbial communities as indicators of ecosystem changes.

Distinct spatiotemporal patterns between fungal alpha and beta diversity of soil-plant continuum in rubber tree

Plant-associated microbial communities strongly relate to host health and productivity. Still, our knowledge of microbial community spatiotemporal patterns in soil-plant continuum is largely limited. Here, we explored the spatiotemporal dynamics of fungal communities across multiple compartments (phyllosphere, leaf endosphere, soil, rhizosphere, rhizoplane, and root endosphere) of rubber tree in two contrasting seasons collected from Hainan Island and Xishuangbanna. Our results demonstrate that the fungal alpha and beta diversity exhibited distinct pattern; the alpha diversity is highly dependent on seasonal changes, while beta diversity only showed a geographical variation pattern. The season-specific environmental factors (e.g., climatic factors) were the most important factors in shaping fungal alpha diversity across the soil-plant continuum. Physicochemical properties explained some of the microbial beta diversity spatiotemporal variation observed, with leaf phosphorus (P) and soil available potassium (AK) likely being the main factors that drove the geographical variation. We further identified the variation of edaphic (e.g., AK) and leaf physicochemical factors (e.g., P) were mainly caused by regional sites (P < 0.05). Taken together, our study provides an empirical evidence that the distinct spatiotemporal patterns of alpha and beta diversity of rubber tree fungal diversity and significantly expand our understanding of ecological drivers of plant-associated microbial communities.

IMPORTANCE

Plants harbor diverse microorganisms in both belowground and aboveground compartments, which play a vital role in plant nitrogen supply and growth promotion. Understanding the spatiotemporal patterns of microbial communities is a prerequisite for harnessing them to promote plant growth. In this study, we show that the alpha and beta diversity of soil-plant continuum in rubber tree exhibited distinct spatiotemporal pattern. Alpha diversity is highly dependent on seasonal changes, while beta diversity only showed a geographical variation pattern. Climatic factors were the most important factors in shaping fungal alpha diversity. Leaf phosphorus (P) and soil available potassium (AK) were major drivers to induce geographical variation.

Dry season temperature and rainy season precipitation significantly affect the spatio-temporal pattern of rubber plantation phenology in Yunnan province

The ongoing global warming trajectory poses extensive challenges to plant ecosystems, with rubber plantations particularly vulnerable due to their influence on not only the longevity of the growth cycle and rubber yield, but also the complex interplay of carbon, water, and energy exchanges between the forest canopy and atmosphere. However, the response mechanism of phenology in rubber plantations to climate change remains unclear. This study concentrates on sub-optimal environment rubber plantations in Yunnan province, Southwest China. Utilizing the Google Earth Engine (GEE) cloud platform, multi-source remote sensing images were synthesized at 8-day intervals with a spatial resolution of 30-meters. The Normalized Difference Vegetation Index (NDVI) time series was reconstructed using the Savitzky-Golay (S-G) filter, coupled with the application of the seasonal amplitude method to extract three crucial phenological indicators, namely the start of the growing season (SOS), the end of the growing season (EOS), and the length of the growing season (LOS). Linear regression method, Pearson correlation coefficient, multiple stepwise regression analysis were used to extract of the phenology trend and find the relationship between SOS, EOS and climate factors. The findings demonstrated that 1) the phenology of rubber plantations has undergone dynamic changes over the past two decades. Specifically, the SOS advanced by 9.4 days per decade (R2 = 0.42, p< 0.01), whereas the EOS was delayed by 3.8 days per decade (R2 = 0.35, p< 0.01). Additionally, the LOS was extended by 13.2 days per decade (R2 = 0.55, p< 0.01); 2) rubber phenology demonstrated a notable sensitivity to temperature fluctuations during the dry season and precipitation patterns during the rainy season. The SOS advanced 2.0 days (r =-0.19, p< 0.01) and the EOS advanced 2.8 days (r =-0.35, p< 0.01) for every 1°C increase in the cool-dry season. Whereas a 100 mm increase in rainy season precipitation caused the SOS to be delayed by 2.0 days (r = 0.24, p< 0.01), a 100 mm increase in hot-dry season precipitation caused the EOS to be advanced by 7.0 days (r =-0.28, p< 0.01); 3) rubber phenology displayed a legacy effect of preseason climate variations. Changes in temperature during the fourth preseason month and precipitation during the fourth and eleventh preseason months are predominantly responsible for the variation in SOS. Meanwhile, temperature changes during the second, fourth, and ninth preseason months are primarily responsible for the variation in EOS. The study aims to enhance our understanding of how rubber plantations respond to climate change in sub-optimal environments and provide valuable insights for sustainable rubber production management in the face of changing environmental conditions.