Effects of Elevated Atmospheric CO2 Concentration and Nitrogen Addition on Element Concentration and Resorption in Leaves of Two Tree Species Under Cadmium Pollution

Abstract:

In order to investigate the effects of cadmium (Cd) pollution and its combinations with elevated atmospheric CO₂ concentration and nitrogen (N) addition on N and phosphorus (P) utilization strategies and Cd accumulation in leaves, two afforestation tree species (Acacia auriculiformis and Cinnamomum camphora) were selected, and the open-top chambers (OTCs) was used to construct the simulated experimental forests of the two tree species. The five treatments were control (CK), adding Cd [10 kg Cd/(hm²·a)] (Cd), adding Cd and CO₂ (700 μmol/mol) (CdC), adding Cd and N [100 kg N/(hm²·a)] (CdN), adding Cd, CO₂ and N (CdCN). After treatment for about 2.5 years, the mature and senescent leaves of two tree species were collected to measure the concentrations of N, P and Cd. The results showed that the foliar P concentration and P resorption efficiency had no significant changes under different treatments, but the N concentration and N resorption efficiency in leaves were significantly affected. The N concentration in leaves of two species increased under CdN treatment, and the N resorption efficiency in C. camphora leaves decreased significantly under Cd and CdN treatments. Under the treatments of Cd, CdC, CdN and CdCN, the Cd accumulation in leaves of two species, as well as the Cd/N and Cd/P ratios in mature leaves of C. camphora increased. The N and P resorption efficiencies were significantly higher, while the Cd accumulation was significantly lower in A. auriculiformis than those in C. camphora. It was demonstrated that the fast-growing leguminous N-fixing tree species (A. auriculiformis) had better N and P utilization strategies and stronger resistance to Cd accumulation than the common non-N-fixing tree species (C. camphora), suggesting that A. auriculiformis could be suitable for ecological restoration in Cd polluted forest sites.