Co-regulation of photosynthetic capacity by nitrogen, phosphorus and magnesium in a subtropical Karst forest in China

Abstract

Leaf photosynthetic capacity is mainly constrained by nitrogen (N) and phosphorus (P). Little attention has been given to the photosynthetic capacity of mature forests with high calcium (Ca) and magnesium (Mg) in the Karst critical zone. We measured light-saturated net photosynthesis (Asat), photosynthetic capacity (maximum carboxylation rate [Vcmax], and maximum electron transport rate [Jmax]) as well as leaf nutrient contents (N, P, Ca, Mg, potassium [K], and sodium [Na]), leaf mass per area (LMA), and leaf thickness (LT) in 63 dominant plants in a mature subtropical forest in the Karst critical zone in southwestern China. Compared with global data, plants showed higher Asat for a given level of P. Vcmax and Jmax were mainly co-regulated by N, P, Mg, and LT. The ratios of Vcmax to N or P, and Jmax to N or P were significantly positively related to Mg. We speculate that the photosynthetic capacity of Karst plants can be modified by Mg because Mg can enhance photosynthetic N and P use efficiency.

The strategies of water–carbon regulation of plants in a subtropical primary forest on karst soils in China

“…Soil texture is silt clay loam, and soil PH is 6.80 ± 0.16 (Chang et al, 2018). The total nitrogen and phosphorus content in soil is 7.30 ± 0.66 and 1.18 ± 0.35 g Kg −1 , respectively, which was similar with that of non-karst CZs (Wang et al, 2018). However, the soil quantities (16.04-61.89 Kg m −2 ) and nitrogen and phosphorus storage (12.04 and 1.68 t hm −2 ) is much lower than that of non-karst CZs, due to the thin and heterogeneous soil layer (Jobbagy and Jackson, 2000;He et al, 2008;Li et al, 2007;Lu et al, 2010).…”

“…The typical vegetation type is mixed evergreen and broadleaf deciduous primary forest, dominated by Itea yunnanensis Franch., Carpinus pubescens Burk., and Lithocarpus confinis Huang., etc. (Wang et al, 2018).…”

“…Leaf mass per area (LMA) was calculated by dividing the corresponding dry mass by leaf area. Finally, leaf density (LD) was calculated by dividing the corresponding LMA by LT. More details are given in Wang et al (2018).…”

“…Three methods are most commonly used for g m estimation. Those methods have been reviewed by Warren (2006) and Pons et al (2009). Briefly, g m can be calculated by the stable isotope method (Evans, 1983;Sharkey et al, 1991;Loreto et al, 1992), the J method (Bongi and Loreto, 1989;Dimarco et al, 1990;Harley et al, 1992;Epron et al, 1995;Laisk et al, 2005), and the "curve-fitting" method (Ethier and Livingston, 2004;Sharkey et al, 2007).…”

“…Briefly, g m can be calculated by the stable isotope method (Evans, 1983;Sharkey et al, 1991;Loreto et al, 1992), the J method (Bongi and Loreto, 1989;Dimarco et al, 1990;Harley et al, 1992;Epron et al, 1995;Laisk et al, 2005), and the "curve-fitting" method (Ethier and Livingston, 2004;Sharkey et al, 2007). All of these methods are based on gas-exchange measurements (Pons et al, 2009), and some common assumptions (Warren, 2006). Thus, the accuracy of each method is unknown to some extent (Warren, 2006).…”