The impact of intensive management on net ecosystem productivity and net primary productivity of a Lei bamboo forest

Abstract

The study of carbon sequestration capacity under intensive management (IM)11IM, intensive management; NIM, non-intensive management; NEP, net ecosystem production; NPP, net primary productivity; GPP, gross primary productivity; EC, eddy covariance; A, the net CO2 assimilation rate for leaf; Vc, Rubisco-limited gross photosynthetic rate; Vj, light-limited gross photosynthesis rate; gs, stomatal conductance; Rd, leaf dark respiration; Acanopy, net CO2 assimilation rates in the canopy; LAI, leaf area index; Rd, leaf dark respiration; Re, ecosystem respiration; Ra, autotrophic respiration; Rm, maintain respiration; Rh, heterotrophic respiration ; Ta_7m, air temperature at 7 m above the ground; Ts_5cm, soil temperature at 5 cm below the ground; rh, relative humidity; vpd, vapor pressure deficit; PPFD, photosynthetic photon flux density measures (such as cutting, thinning, plowing, and fertilization) has become a major issue of carbon budgets in the context of global climate change. Bamboo forest, also known as “the second largest forest in the world,” plays an important role in the carbon cycle. Due to its high economic value, IM practices have been widely used to manage bamboo forests, which in turn may affect the global carbon cycle and carbon budget balance of the ecosystem. However, due to a lack of long-term field experiments and suitable representative models for carbon cycle research in bamboo forests, there is little understanding of the effects of IM measures on carbon sources/sinks in bamboo forest ecosystems at large temporal scales. In this study, we used a representative Lei bamboo (Phyllostachys praecox C.D. Chu & C.S. Chao) forest occurring in Taihuyuan town, Zhejiang Province, China as the study object and a new generation Triplex-Flux model to simulate the net ecosystem productivity (NEP) and net primary productivity (NPP) of the Lei bamboo forest under IM and non­intensive management (NIM) in 2011–2013 and 2015. The aim was to reveal the impact of IM on the carbon cycle of a bamboo forest ecosystem. The results showed that the Triplex-Flux model was suitable for studying the carbon cycle in the Lei bamboo forest. On a 30 min time scale, R2 values ranged between 0.78–0.91 (p<0.01) and the RMSE varied between 0.04–0.09 gC m−1. On a daily scale, the model was also able to simulate the NEP of the Lei bamboo forest (R2>0.42, p<0.001). However, the Triplex-Flux model failed to reveal the NEP patterns, as there were certain deviations between some of the simulated NEP peak and valley values, which were underestimated at noon and overestimated at night. IM played a key role in controlling carbon budget of the Lei bamboo forest. On a seasonal scale, the effect of IM measures was the most significant in spring; harvesting old bamboo wood and removing new shoots caused a 27.71% and 58.52% decrease in NEP and NPP, respectively. Hooking tips and trimming diseased branches had little impact on NEP and NPP (0.02% and 7.27%, respectively) in autumn. On an annual scale, IM measures resulted in average annual decrease in NEP and NPP by 27.20% and 13.72%, respectively. Our findings can provide a reference base that may be applicable to studying the carbon cycle in bamboo forests across the country and even at larger scales.