Litterfall biomass and nutrient cycling in karst and nearby non-karst forests in tropical China: A 10-year comparison.

Litterfall helps maintaining primary production and nutrient cycling in forest ecosystems. However, few studies have investigated long-term characteristics of litterfall in tropical karst and non-karst forests co-occurring in the same region. A 10-year comparative study was conducted to estimate the biomass, litter accumulation, turnover rate, nutrient return and nutrient use efficiency associated with litterfall in a karst forest (KF) and a nearby non-karst forest (NKF) in northern tropical China. Significant spatial-temporal variation was observed in monthly and annual litterfall biomass in the two forests. Annual mean litterfall biomass in KF (9.75 Mg ha year) was obviously lower than that in NKF (10.49 Mg ha year). The litterfall biomass in NKF was significantly correlated with maximum air temperature, wind speed and total solar radiation, whereas that in KF was significantly correlated with relative humidity, wind speed and low temperature. Average stand litter in KF (2.92 Mg ha year) was significantly higher than that in NKF (2.38 Mg ha year). Stand litter mostly occurred during the cool and dry season, which coincided with litterfall input and exhibited bimodal pattern. Turnover rate was 1.3 time higher in NKF than in KF, suggesting that litter decomposed slowly in karst habitats. Distinct temporal dynamic and significant differences were observed in chemical composition of litterfall between KF and NKF. Total amounts of C, P, K and total nutrients returned to the topsoil in KF were significantly lower than those in NKF. The KF exhibited relatively high P and K use efficiency because of their low availability in karst soils. Compared with the non-karst habitat, the tropical karst habitats are more likely to develop a plant community with certain nutrient concentrations of litterfall and with a nutrient cycling mechanism that is well-adapted to harsh and heterogeneous condition.