Photosynthetic carbon fixation capacity of black locust in rapid response to plantation thinning on the semiarid loess plateau in China

Abstract

Black locust (Robinia pseudoacacia L.) has been widely planted throughout the semiarid Loess Plateau in China. However, black locust plantations likely induce stand degradation and soil desiccation because of high water consumption, high stand density, and insufficient stand management. In this study, five kinds of density types in 19-year-old black locust plantations, including three intact non-thinned control plantation types with different stand densities (1800, 2700, and 3600 trees ha −1 ) and two thinned-treatment plantation types with the same stand densities (1800 trees ha −1 ) were selected to calculate the responses to thinning intensity in the Maliantan catchment within the central Loess Plateau. Gas exchange, leaf area index, associated changes in the photosynthetic carbon fixation capacity (PCFC), and environmental variables (light radiation, air temperature, and soil moisture) were determined throughout the growing season in 2009. The growth, daily leaf-level net CO2 assimilation rate (An), and tree-level PCFC were significantly different among the three intact black locust plantations in their annual growth period. An and PCFC increased as the stand density decreased because of enhanced environmental resource availabilities per individual tree, including the increased exposure to light radiation, canopy air temperature, and soil moisture level. Comparing thinned and non-thinned black locust plantations, we provided ecophysiological evidence that black locust trees could actively adjust their photosynthetic functions from the beginning of the first growing season after thinning to enhance their height, diameter, and canopy diameter during growth and development. This mechanism indicated that the rapid adaptability of black locust in response to plantation thinning on the semiarid Loess Plateau. Based on the same stand density (1800 trees ha −1 ), the low thinning intensity of 33% was more suitable for the sustainable management and increased of photosynthetic carbon fixation capacities of black locust trees on the Loess Plateau in China. These findings can enrich our knowledge of forest plantation dynamics and provide valuable information regarding sustainable plantation management in this ecological fragile region.

Relative importance of soil properties and functional diversity to the spatial pattern of the forest soil nitrogen

“…High LAI significantly increased canopy interception of rainfall, significantly reduced surface runoff and soil erosion, and thus reduced surface nitrogen leaching loss (Malek 2010, Mohammed andTarboton 2016). However, some studies also found that when LAI decreased due to thinning, the content of SN increased (Jonsson and Sigurdsson 2010, Garcia-Prats et al, 2018, Zheng et al, 2019; an explanation might be that large amounts of litter enter the soil during thinning. PAR was a source of energy for plant life activities and organic matter synthesis, and it increased transpiration in plants and allowed more soil nitrogen to be transported upwards with water to the leaves (Ward et al, 2013.…”

Effects of Stand Density on Growth, Soil Water Content and Nutrients in Black Locust Plantations in the Semiarid Loess Hilly Region

“…For instance, stand density strongly affects the amount of available growth space in the community and natural resources available to a single tree [25,26]. A black locust plantation with higher density can capture more light energy through a higher leaf area index (LAI) and canopy density, and has stronger photosynthetic carbon fixation capacity [27]. However, high stand density would also intensify the competition for space and resources of single trees [28,29], which is not conducive to stand growth.…”

“…The samplings in the above study cases are diverse in plot ages and management background. Some studies focused on the influences of intermediate cutting on high density stands [27,39,46]. In this study, by setting up fixed plots with a similar stand age and land-use background, we comparatively investigated the characteristics of growth, soil water content, and nutrient conditions for the black locust plantations with density gradients.…”

The effects of crop tree thinning intensity on the ability of dominant tree species to sequester carbon in a temperate deciduous mixed forest, northeastern China

“…Many studies have examined the effects of thinning on carbon stocks (del Río et al, 2017;Lin et al, 2018;Schaedel et al, 2017;Shuyong et al, 2017), but previous results remain inconsistent. The rapid regeneration of understory vegetation and the fast growth of post-thinning survivors could lead to greater carbon sequestration rates (Briceño et al, 2006;Hoover and Stout, 2007;López et al, 2003;Schilling et al, 1999;Zheng et al, 2019). Longer rotation may also enhance carbon sequestration, because it allows the biomass production to recover to avoid making the forest a net carbon source (Kaipainen et al, 2004;Nepstad et al, 1999).…”