Rates of litter decomposition and soil respiration in relation to soil temperature and water in different-aged Pinus massoniana forests in the Three Gorges Reservoir Area, China

Abstract

To better understand the soil carbon dynamics and cycling in terrestrial ecosystems in response to environmental changes, we studied soil respiration, litter decomposition, and their relations to soil temperature and soil water content for 18-months (Aug. 2010-Jan. 2012) in three different-aged Pinus massoniana forests in the Three Gorges Reservoir Area, China. Across the experimental period, the mean total soil respiration and litter respiration were 1.94 and 0.81, 2.00 and 0.60, 2.19 and 0.71 µmol CO2 m(-2) s(-1), and the litter dry mass remaining was 57.6%, 56.2% and 61.3% in the 20-, 30-, and 46-year-old forests, respectively. We found that the temporal variations of soil respiration and litter decomposition rates can be well explained by soil temperature at 5 cm depth. Both the total soil respiration and litter respiration were significantly positively correlated with the litter decomposition rates. The mean contribution of the litter respiration to the total soil respiration was 31.0%-45.9% for the three different-aged forests. The present study found that the total soil respiration was not significantly affected by forest age when P. masonniana stands exceed a certain age (e.g. >20 years old), but it increased significantly with increased soil temperature. Hence, forest management strategies need to protect the understory vegetation to limit soil warming, in order to reduce the CO2 emission under the currently rapid global warming. The contribution of litter decomposition to the total soil respiration varies across spatial and temporal scales. This indicates the need for separate consideration of soil and litter respiration when assessing the climate impacts on forest carbon cycling.

Figure 1. Seasonal patterns and monthly dynamics of the total soil respiration (•), litter respiration (○), and the litter-free soil respiration (▾) in different-aged Pinus massoniana forests (mean ±1SD, n = 9).

Figure 2. Observed (•) and predicted (○) values of litter dry mass remaining across the experimental period in different-aged Pinus massoniana forests (mean ±1SD, n = 9).

Figure 3. Relationships between mean monthly litter decomposition and the total soil respiration (a), litter respiration (b), and litter-free soil respiration rate (c) for different-aged Pinus massoniana forests.

Note: respiration rate is the mean value across the litter decomposition period.

Figure 4. Soil temperature (5 cm soil depth), soil water content (5 cm soil depth) and litter water content in different-aged Pinus massoniana forests studied across the experiment period.

Figure 5. Relationships between the total soil respiration (a, b), litter respiration (c, d), litter-free soil respiration (e, f) and soil temperature at 5 cm depth or soil water content at 5 cm depth in different-aged Pinus massoniana forests during the 18-months field observations.

Figure 6. Relationships between litter decomposition (%) and soil temperature (a) or soil water content (b) in different-aged Pinus massoniana forests.