Variation patterns of fine root biomass, production and turnover in Chinese forests

China's forests cover 208.3 million ha and span a wide range of climates and a large variety of forest types, including tropical, temperate, and boreal forests. However, the variation patterns of fine root (< 2 mm in diameter) biomass, production, and turnover from the south to the north are unclear. This study summarizes fine root biomass (FRB), production (FRP) and turnover rate (FRT) in China's forests as reported by 140 case studies published from 1983 to 2014. The results showed that the mean values of FRB, FRP and FRT in China's forests were 278 g m(-2), 366 g m(-2) a(-1), and 1.19 a(-1), respectively. Compared with other studies at the regional or global scales, FRB in China's forests was lower, FRP was similar to estimates at the global scale, but FRT was much higher. FRB, FRP, and FRT in China's forests increased with increasing mean annual precipitation (MAP), indicating that fine root variables were likely related to MAP, rather than mean annual temperature or latitude. This is possibly due to the small variation in temperature but greater variation in precipitation during the growing season. These findings suggest that spatiotemporal variation in precipitation has a more profound impact on fine root dynamics in China's forests, and this will impact carbon and nutrient cycles driven by root turnover in the future.

Estimation of fine root production, mortality and turnover with Minirhizotron in Larix gmelinii and Fraxinus mandshurica plantations

Fine root turnover is a major pathway for carbon and nutrient cycling in forest ecosystems.However,to estimate fine root turnover,it is important to first understand the fine root dynamic processes associated with soil resource availability and climate factors.The objectives of this study were:(1)to examine patterns of fine root production and mortality in different seasons and soil depths in the Larix gmelinii and Fraxinus mandshurica plantations,(2)to analyze the correlation of fine root production and mortality with environmental factors such as air temperature,precipitation,soil temperature and available nitrogen,and(3)to estimate fine root turnover.We installed 36 Minirhizotron tubes in six monospecific plots of each species in September 2003 in the Mao’ershan Experimental Forest Station.Minirhizotron sampling was conducted every two weeks from April 2004 to April 2005.We calculated the average fine root length,annual fine root length production and mortality using image data of Minirhizotrons,and estimated fine root turnover using three approaches.Results show that the average growth rate and mortality rate in L.melinii were markedly smaller than in F.mandshurica,and were highest in the surface soil and lowest at the bottom among all the four soil layers.The annual fine root production and mortality in F.mandshurica were significantly higher than in L.gmelinii.The fine root production in spring and summer accounted for 41.7% and 39.7% of the total annual production in F.mandshurica and 24.0% and 51.2% in L.gmelinii.The majority of fine root mortality occurred in spring and summer for F.mandshurica and in summer and autumn for L.gmelinii.The turnover rate was 3.1 a^(-1) for L.gmelinii and 2.7 a^(-1) for F.mandshurica.Multiple regression analysis indicates that climate and soil resource factors together could explain 80% of the variations of the fine root seasonal growth and 95%of the seasonal mortality.In conclusion,fine root production and mortality in L.gmelinii and F.mandshurica have different patterns in different seasons and at different soil depths.Air temperature,precipitation,soil temperature and soil available nitrogen integratively control the dynamics of fine root production,mortality and turnover in both species.

Fine Roots Dynamics in Two Forest Strata of a Semi-Deciduous Forest in Northern Republic of Congo

The belowground biomass is represented by coarse and fine roots. Concentrated in the superficial horizons of the soil, the fine roots play a crucial role in the functioning of a forest ecosystem. However, studies on their dynamics in natural forests are almost non-existent in the Republic of Congo. Here, we estimated the biomass, production, turnover and fine root lifespan of two forest strata of a semi-deciduous forest: the Gilbertiodendron dewevrei (De Wild.) J. Léonard forest (GF) and the mixed forest (MF) of land. The ingrowth cores method was used to estimate the biomass, production, turnover and lifespan of fine roots. The results of this study revealed that the biomass, production and fine root turnover of the two forest strata studied significantly decreased with increasing soil depth, with an increase in lifespan. The annual fine root biomass of GF (2284.50 ± 37.62 and 1034.61 ± 14.52 ) was slightly lower than that of MF (2430.07 ± 40.68 and 1043.10 ± 11.75 ) in the 0-15 cm and 15-30 cm horizons, respectively. The annual production of fine roots from these latter horizons was respectively 1300.19 ± 32.17 and 539.18 ± 11.55 in GF and 1362.24 ± 39.59 and 492.95 ± 14.38 in the MF. Root turnover was higher in the GF (1.68 ± 0.05 and 1.35 ± 0.03 ) than in the MF (1.57 ± 0.05 and 1.13 ± 0.02 ). The lifespan of fine roots increased with the depth of the soil. The difference in fine root dynamics observed between the forest strata studied was influenced by the Evenness index and the above-ground biomass.