Robinia pseudoacacia decline and fine root dynamics in a plantation chronosequence in the Yellow River Delta, China

Abstract

Fine roots (<2 mm in diameter) play a significant role in tree growth and stand productivity. However, knowledge of fine root dynamics in saline alkali soil remains limited. Using sequential soil core and ingrowth core methods, we assessed the dynamics of aboveground biomass (AGB) and production (AGP), fine root biomass (FRB), production (FRP) and turnover (FRT), and soil properties (water content [SWC], salt content [SSC], pH and nutrients) in 2-, 18-, 32- and 42-year-old black locust (Robinia pseudoacacia L.) stands in the Yellow River Delta, China. Corresponding to the unimodal growth pattern in AGP, the AGB of black locust rapidly increased until age 32 and then slowed down. In contrast, across all depths, FRB and FRP took a unimodal pattern with a decrease in growth around age 32, and FRT continually decreased with stand age. SWC and soil nutrients increased with stand age, whereas SSC and pH decreased with stand age until age 32 and then increased. Based on the correlation analysis, we may presume that in addition to the age effect, the decline of black locust in AGP is most likely caused by SWC, SSC, and pH stresses through the dysfunction in nutrient absorption by fine roots. Study Implications: In recent decades, the rapidly increasing plantations in the Yellow River Delta of China as elsewhere have brought enormous economic and ecological benefits. However, afforestation in the Yellow River Delta is complex due to soil salinity and unique soil water and nutrient dynamics. The most extensive Robinia pseudoacacia plantations have shown a noticeable decline. Fine root dynamics affected by soil environments and stand age play a significant role in tree growth and stand productivity. Our study illustrates the general growth patterns of tree growth and fine root dynamics of R. pseudoacacia plantations under salt stress and related to soil environments (nutrients, moisture, salinity) in the Yellow River Delta, China. Young and middle-aged R. pseudoacacia plantations could reduce soil salt content although soil salt content and pH increased again after the plantations reached a certain age (42 years in this study). The increase in soil salt content greatly limited fine root biomass and tree growth. As a result, thinning stands at an appropriate time (after 32 years in this study) and relevant engineering measures to reduce soil salt content should be carried out to improve fine root growth and stand productivity. In addition, replacing old R. pseudoacacia stands that suffer severe decline and mortality with new plantations will be necessary for sustainable management of plantations and maintaining a reasonably high level of forest productivity in coastal saline-alkali areas.

Carbon sequestration and soil nitrogen enrichment in Robinia pseudoacacia L. post-mining restoration plantations

“…Still, it is important to note that all abovementioned studies refer to young plantations (<25 years old) that have not been subjected to any forest management practices yet. Black locust reaches maturity at the age of 25-30 years, while growth and ABG production is levelling off after that age, as observed at other degraded sites (Wang et al, 2015;Guo et al, 2022) and at our study site (Manolopoulos et al, 2022). Based on these, we assumed an average age for stand maturity at 27.5 years and we estimated that the current total above-ground biomass of the plantations (28.5 t ha −1 ; Figure 2) at a mean age of 16 years, represents less than 40% of the total AGB at maturity, which is expected to reach at least 80.0 t ha −1 if the linear increase with time (Figure 4A) continues until that age.…”

“…Although they constitute a minor carbon stock due to their small contribution to the total root biomass (Vogt et al, 1995), fine roots fuel the soil organic carbon and promote carbon cycling (Gill and Jackson, 2000;Helmisaari et al, 2002). We estimated a low C flux in fine root annual production (0.17 t C ha −1 yr −1 ; Supplemental Table 1), compared to other black locust restoration plantations of approximately the same age (Guo et al, 2022) and temperate forest ecosystems (Gill and Jackson, 2000;Brunner and Godbold, 2007;Finér et al, 2011). On the contrary, the fine root turnover rate of the studied black locust (0.62 yr −1 ) was higher compared to others (Guo et al, 2022), indicating that fine roots at the lignite complex of NW-Greece form a smaller but faster regenerated carbon flux.…”

“…We estimated a low C flux in fine root annual production (0.17 t C ha −1 yr −1 ; Supplemental Table 1), compared to other black locust restoration plantations of approximately the same age (Guo et al, 2022) and temperate forest ecosystems (Gill and Jackson, 2000;Brunner and Godbold, 2007;Finér et al, 2011). On the contrary, the fine root turnover rate of the studied black locust (0.62 yr −1 ) was higher compared to others (Guo et al, 2022), indicating that fine roots at the lignite complex of NW-Greece form a smaller but faster regenerated carbon flux. Decomposition of all the above-mentioned compartments have added carbon input to the forest floor and have fueled soil organic carbon.…”

Mangrove forest utilization policies reconceptualized with a view to improving the regional economy in Aceh Tamiang District, Indonesia

“…On the east coast of Aceh Province, the Aceh Tamiang District is home to the largest mangrove forest, which supports several protected ecosystems and wild animals (Ely et al 2021;Guo et al 2022;Yunianto and Kurniawan 2022). Even though they are currently in poor shape as a result of mangrove land being converted to fulfill the demands of the neighborhood, all kinds of natural resources in the mangrove area generally provide advantages for the community (Osorio et al 2017;Firdaus et al 2021;Adnan et al 2022).…”

Salt Addition Mitigate Mortality Risk and Prolong Survival of Robinia pseudoacacia Subjected to Drought Stress

“…on 2 September 2022. A total of 20 seedings were subjected to salt irrigation until the soil salinity reached 0.3%, which is considered the salinity tolerance threshold for Robinia pseudoacacia [37,38]. The irrigation schedule for salt stress was as follows: 1 L 100 mM NaCl on 2 September 2022; 1 L 150 mM NaCl on 6 September 2022; 1 L 200 mM NaCl on 12 September 2022; and 1 L 250 mM NaCl on 17 September 2022.…”