Temperature drives global patterns in forest biomass distribution in leaves, stems, and roots

Abstract

Whether the fraction of total forest biomass distributed in roots, stems, or leaves varies systematically across geographic gradients remains unknown despite its importance for understanding forest ecology and modeling global carbon cycles. It has been hypothesized that plants should maintain proportionally more biomass in the organ that acquires the most limiting resource. Accordingly, we hypothesize greater biomass distribution in roots and less in stems and foliage in increasingly arid climates and in colder environments at high latitudes. Such a strategy would increase uptake of soil water in dry conditions and of soil nutrients in cold soils, where they are at low supply and are less mobile. We use a large global biomass dataset (>6,200 forests from 61 countries, across a 40°C gradient in mean annual temperature) to address these questions. Climate metrics involving temperature were better predictors of biomass partitioning than those involving moisture availability, because, surprisingly, fractional distribution of biomass to roots or foliage was unrelated to aridity. In contrast, in increasingly cold climates, the proportion of total forest biomass in roots was greater and in foliage was smaller for both angiosperm and gymnosperm forests. These findings support hypotheses about adaptive strategies of forest trees to temperature and provide biogeographically explicit relationships to improve ecosystem and earth system models. They also will allow, for the first time to our knowledge, representations of root carbon pools that consider biogeographic differences, which are useful for quantifying whole-ecosystem carbon stocks and cycles and for assessing the impact of climate change on forest carbon dynamics.allocation | biomass fraction | root:shoot | allometry | biogeography A fter acquisition via photosynthesis (gross primary production), new plant carbon (C) is respired, transferred to mycorrhizal symbionts, exuded, or converted into new biomass (net primary production). The new biomass can be foliage, stems (including boles, branches, and bark), roots, or reproductive parts. The proportional allocation of new C to these four plant biomass pools, when combined with their turnover rates, results in the proportional distribution of standing biomass among these pools. Such processes can be influenced by plant size, resource supply, and/or climate (1-10). Although simple in concept, our understanding of these processes and our ability to quantify and predict them remain surprisingly rudimentary (3-13).The general lack of knowledge about C partitioning is important for a number of reasons, including its implications for the accuracy of global C cycle modeling and accounting. A recent study (11) concluded different carbon partitioning schemes resulted in large variations in estimates of global woody carbon flux and storage, indicating that stand-level controls on carbon partitioning are not yet accurately represented in ecosystem models.

Biogeographic variation in evergreen conifer needle longevity and impacts on boreal forest carbon cycle projections

“…Similarly, it is likely that low temperatures and dry conditions both contribute to high carbon allocation below ground in colder forests (25,26). For the study sites on either continent, MAT was correlated strongly with mean annual precipitation (MAP), as well as with seasonal climate metrics and with the ratio between MAP and potential evapotranspiration.…”

“…Given this, and that our goal includes assessing ecosystem impacts of changes in foliage turnover rate, we jointly examine impacts of temperature-sensitive biomass distribution (26) on CABLE predictions. Our modification of the biomass distribution in CABLE is based on analyses that show that foliage and roots represent a greater and smaller fraction, respectively, of total biomass in forests in increasingly cold environments (26), which is consistent with independent data showing proportionally greater carbon allocation below ground for Picea in colder, drier habitats (25). Incorporating temperature-dependent biomass partitioning yields the result that allocation of new biomass (NPP) to needles must be markedly low in the cold far north (Fig.…”

Climate modifies response of non-native and native species richness to nutrient enrichment

“…Precipitation, temperature and water availability are three of the most common variables used to understand how climate shapes species distributions, diversity and trait variation [24,37,41]. Further, these three variables impact on plants' photosynthetic capacity, growth rates and biomass allocation [41,42].…”

Evaluation of MODIS Land Surface Temperature Data to Estimate Near-Surface Air Temperature in Northeast China

“…Accurate estimation of T air and mapping its spatial distribution are useful for predicting ecological consequences of climate change. For example, climate warming will lead to higher temperatures and an increase of extreme weather events, which are associated with changes in wildfire regime [6][7][8], forest biomass distribution [9] and crop yield [10,11]. The demand for accurate spatial T air data over large scale has continued to rise [12,13].…”