Soil-plant-atmosphere interactions: structure, function, and predictive scaling for climate change mitigation

Abstract

Background It is well established that the functioning of terrestrial ecosystems depends on biophysical and biogeochemical feedbacks occurring at the soil-plant-atmosphere (SPA) interface. However, dynamic biophysical and biogeochemical processes that operate at local scales are seldom studied in conjunction with structural ecosystem properties that arise from broad environmental constraints. As a result, the effect of SPA interactions on how ecosystems respond to, and exert influence on, the global environment remains difficult to predict. Scope We review recent findings that link structural and functional SPA interactions and evaluate their potential for predicting ecosystem responses to chronic environmental pressures. Specifically, we propose a quantitative framework for the integrated analysis of three major plant functional groups (evergreen conifers, broadleaf deciduous, and understory shrubs) and their distinct mycorrhizal symbionts under rising levels of carbon dioxide, changing climate, and disturbance regime. First, we explain how symbiotic and competitive strategies involving plants and soil microorganisms influence scale-free patterns of carbon, nutrient, and water use from individual organisms to landscapes. We then focus on the relationship between those patterns and structural traits such as specific leaf area, leaf area index, and soil physical and chemical properties that constrain root connectivity and canopy gas exchange. Finally, we use those relationships to predict how changes in ecosystem structure may affect processes that are important for climate stability. Conclusions On the basis of emerging ecological theory and empirical biophysical and biogeochemical knowledge, we propose ten interpretive hypotheses that serve as a primary set of hierarchical relationships (or scaling rules), by which local SPA interactions can be spatially and temporally aggregated to inform broad climate change mitigation efforts. To this end, we provide a series of numerical formulations that simplify the net outcome of complex SPA interactions as a first step towards anticipating shifts in terrestrial carbon, water, and nutrient cycles.

A record of vapour pressure deficit preserved in wood and soil across biomes

“…The relationship between VPD and plant δ 13 C:δ 18 O ratios is complex and many processes are at play, most notably photosynthetic capacity, stomatal conductance, RuBisCO fractionation, and the amount, type and timing of water inputs, all of which have been shown to alter δ 13 C values or δ 18 O values or both 3 , 8 , 12 , 57 . We therefore do not expect that a single mechanism would adequately explain the consistent increase in the isotope ratios in plant molecules and pedogenic carbonates.…”

“…VPD is often monitored as a proxy for plant water stress because it is a principal control on stomatal water loss and photosynthetic carbon fixation 2 . VPD is not a meteorological parameter for climate studies because it is a relative metric of stress that varies among plant species, as inferred from their leaf functional traits, and from interactions between roots, soils, and microorganisms in the rhizosophere, which together govern responses to climate at local to global scales 3 – 5 . However, VPD does reflect the effect of temperature and precipitation on relative humidity 6 and transpiration demand, which stimulates stomatal closure to minimize water loss, and thus the flow of water and nutrients from the soil through plants and ultimately to the atmosphere 7 , 8 .…”

Sixteen hundred years of increasing tree cover prior to modern deforestation in Southern Amazon and Central Brazilian savannas

“…Our observation of increasing tree cover coincides with the chronology of intensification in sedentary settlements during the late Holocene, which probably resulted in an overall decline in deforestation and fire use across the region prior to European contact. On the other hand, current deforestation is interrupting a historical increase in tree cover in forests and savannas, which would have been further accelerated by the recent stimulation of tree growth due to increases in atmospheric CO 2 (Silva & Lambers, 2020). Moreover, current deforestation is also likely to change the regional climate by decreasing rainfall.…”

“…To better understand whether and how changes in forest and savanna cover influence soil carbon stocks, we quantified soil carbon concentrations at each study site profile and soil depth. To better estimate the timing of vegetation change and its resulting effects on soil carbon stocks, bulk density (g/cm 3 ) from a subset of typical forest, savanna, and transition ecosystems were supplemented by radiocarbon and stable isotope datasets from previously published studies conducted in central Brazil (Silva et al., 2008, 2010, 2013). To match the analysis of ecosystem cover (described above) we report carbon stocks down to 80 cm at all sites.…”

From Trees to Ecosystems: Spatiotemporal Scaling of Climatic Impacts on Montane Landscapes Using Dendrochronological, Isotopic, and Remotely Sensed Data

“…Additionally, based on the recent indications that winter NDVI is coupled with P. hartwegii 's ring width in this region (Correa‐Díaz et al, 2019), we hypothesize that wood 13 C and 18 O isotopic signatures are linked to a specific NDVI time period characterized by temperature effects on photosynthetic activity or drought effects on transpiration (del Castillo et al, 2015). If these hypotheses hold true, scaling functions might be devised to predict climate responses from tree to landscapes (Silva & Lambers, 2020).…”