Abstract
The biomass estimation, nutrient stock, and stoichiometric characteristics are critical for understanding forest productivity and quality. To date, there is not enough comprehensive research on nutrient stock and stoichiometric characteristics of each tissue among different tree species in the semi-arid region on the Loess Plateau. So, six dominant tree species were selected to estimate the forest biomass by allometric equation and to analyze the effects of tissue and species on biomass allocation and nutrient stock by variance analysis in our study. Results showed that forest biomass, nutrient concentration, nutrient stock, and stoichiometric characteristics varied with tissue and species. Betula platyphylla and Pinus tabulaeformis had high total biomass while Populus davidiana had the least total biomass, and the biomass allocation of each tissue generally followed the order of stem > branch > root > foliage. The weighted mean concentrations of carbon (C), nitrogen (N), and phosphorus (P) changed from 432.67 g·kg−1 to 481.43 g·kg−1, from 6.15 to 8.30 g·kg−1, and from 0.43 to 0.74 g·kg−1, respectively. The relatively high nutrient stocks were observed in Pinus tabulaeformis and Betula platyphylla across organs and in stem across species. The C:N and C:P ratios were higher in stem and root than those in branch and foliage for each species, while the effects of tissue on N:P varied with species. Overall, the N:P ranged from 7.92 for stem (Larix principis-rupprechtii) to 22.18 for foliage (Populus davidiana). Therefore, Pinus tabulaeformis and Betula platyphylla can increase effectively nutrient fixation capacity in the semi-arid region on the Loess Plateau. Also, N or P limitation of tree growth in this region varied with species.
Highlights
The Loess Plateau is one of the most seriously eroded regions in the world with a fragile ecological environment and human deforestation and overgrazing [1,2]
Our study showed that the weighted mean carbon concentration in the transition region between semi-arid and sub-humid areas on the Loess Plateau varied from 432.67 g·kg−1 for Quercus wutaishanica to 481.43 g·kg−1 for Pinus armandii, a narrower range than that for 10 species in northeastern China [20]
The results indicated that Betula platyphylla and Pinus tabulaeformis had high capacity to fix carbon and nutrient, which could be widely planted to increase the ecological functions of forest ecosystem
Summary
The Loess Plateau is one of the most seriously eroded regions in the world with a fragile ecological environment and human deforestation and overgrazing [1,2]. The Natural Forest Protection Program and the Grain-to-Green Program have been implemented to improve environments and foster sustainability of ecosystem services [3,4,5]. Of biomass in forests restored from farmlands in the Loess. Limiting our ability of evaluating forest ecosystem productivity and services. Tree biomass is an important indicator to evaluate forest carbon sequestration [7] and soil erosion controls [3]. Nutrient contents (including carbon (C), nitrogen (N), and phosphorus (P)) play a major, irreplaceable role in plant growth and a variety of physiological activities [8], which provide the basis for assessing forest productivity and services [9]. Forest biomass, nutrient concentration, and stoichiometric characteristics of C, N, and P [10,11] have increasingly become the current research hotspots
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