Effects Of Forest Gaps On The Ecological Chemometric Characteristics Of Litter-Soil In Pinus Densiflora Sieb.and Robinia Pseudoacacia L.Forests

The Mountain Tai and Mountain Yimeng(Taiyi Mountain area)is a representative region located in the rocky mountainous area of northern China,and is also a key area for national soil and water conservation projects.Pinus densiflora Sieb.(PDS)and Robinia pseudoacacia L.(RPL)forests are typical ecological afforestation tree species in the region.However,the presence of a single type of forest structure,excessive initial planting density,as well as human factors and natural disasters have led to the formation of forest gaps.Forest gaps play an important role in the biogeochemical cycle,ecological function,and stability of forest ecosystems.To explore the impact of forest gaps on the litter-soil ecological chemometric characteristics of PDS and RPL forests in the Taiyi Mountain Area,and to reveal the impact mechanism of forest gaps on nutrient cycling in PDS and RPL forests ecosystems.In this paper,the Huangqian watershed in a typical area of the Taiyi Mountains is taken as the research area,and the gap and non-gap woodlands of PDS and RPL forests in the watershed are taken as the research objects.Using the methods of field fixed point sampling and indoor quantitative analysis,and applying the theory of ecological chemometrics,we conducted a systematic study of the soil physical and chemical properties,litter-soil ecological chemometric characteristics,growing season dynamics,and correlations in gaps of PDS and RPL forests.The research results can provide a scientific basis for the study of the ecological chemometrics impact mechanism of forest gaps on artificial forest systems,and offer scientific and technological support for forest vegetation restoration and sustainable management in the Taiyi Mountains.The research results are as follows:(1)Forest gaps have a significant impact on the carbon(C),nitrogen(N),and phosphorus(P)content,as well as ecological chemometric characteristics,of the litter in PDS and RPL forests.Compared to non-gap,the N content and N:P ratio of litter increased significantly,while the C content,C:N ratio,and C:P ratio decreased significantly in the gaps of PDS forests.The C and P contents of litter increased significantly in the gaps of RPL forest.In the gap center(GC)and gap edge(GE)of PDS forest,the N content increased significantly,while the C content and C:N ratio decreased significantly in the litter;Additionally,the C:P ratio of litter in the GC decreased significantly.In the GC of RPL forest,the C,N contents and N: P ratio of litter increased significantly,while the C:N ratio decreased significantly.In the GC,the N content in the litter of PDS and RPL increased by 14.46% and37.59%,respectively,while the C: N content decreased by 30.11% and 22.23%,respectively.Lower C: N will accelerate the decomposition of apoplastic material,so the decomposition of apoplastic material in the GC is faster,increasing soil fertility and promoting nutrient cycling in the subsurface soil ecosystem.(2)Forest gaps can effectively improve the soil physical properties of PDS and RPL forests.Compared with non-gap,the bulk density and sand content significantly decreased,while the total porosity,non capillary porosity,clay and silt content significantly increased of the soil in the gap of PDS forest.The bulk density decreased significantly,while the total porosity,capillary porosity,and water content increased significantly,and the content of clay,silt,and sand particles did not change significantly of the soil in the gaps of the RPL forest.The presence of forest gaps significantly improved the soil physical properties in the 0–20 cm soil layer.In the forest gaps of PDS forests,soil bulk density decreased by 12.32% at the GC and 5.80% at the GE,while clay content increased by 117.98% at the GC and 152.81% at the edge,and silt content increased by 130.04% at the center and 118.90% at the GE.In the forest gaps of RPL forests,soil bulk density decreased by 6.14% at the GC and 5.26% at the edge,while soil moisture content increased by 23.73% at the center and 21.91% at the GE.Total porosity,capillary porosity,clay content,and silt content of the soil at the GC in RPL forests increased by 54.87%,48.78%,39.33%,and 24.14%,respectively.(3)Forest gaps have significant effects on soil C,N,P content and ecological chemometric characteristics in PDS and RPL forests.Compared with non-gap,the soil C,N,and P contents increased significantly,while C: N and C: P decreased significantly,while N: P did not change significantly in gaps of PDS forest.The soil C content and C: P content significantly increased,while P content significantly decreased,while N content and C: N content did not significantly change in the gaps of RPL forest.The contents of soil C,N,and P increased significantly,while C: N and C: P decreased significantly,while N: P did not change significantly in the GC and GE of PDS forest;The content of C,N,and P in the surface soil(0–20 cm)at the GC was significantly higher than that at the GE,respectively increasing by 24.73%,21.68%,and 15.79%.The soil C: P and N: P increased significantly,with a small impact on C: N in the GC and GE in the RPL forest;The C: P and N: P of the surface soil in the GC were significantly higher than those at the GE,increasing by 23.07%and 19.35%,respectively.Therefore,the soil fertility in forest gaps is high,and has a high potential for nutrient supply during plant growth.(4)The C,N,P ecological chemometric characteristics of litter-soil in gaps and non-gap of PDS and RPL forests have significant dynamic changes during the growing season.The C and N contents of litter was higher in the early growing season,but lower in the late growing season,and C: N reaches its maximum value in the late growing season in the gap and non-gap of PDS and RPL;The P content in the litter of PDS reached the highest value in the middle growing season,while C: P and N: P reached the lowest value in the middle growing season;The P content and N: P reached the lowest value in the late growing season,while C:P reached the highest value in the late growing season in the litter of RPL.The C content,C:P,and N: P of soil were lower in the late growing season,while the N content was higher in the early growing season,with no significant change in C: N in gaps and non-gap of PDS and RPL;The soil P content of PDS reached the lowest value in the middle growing season;The soil P content of RPL reached its maximum in the late growing season.The seasonal variation trend of C and N content in litter-soil is similar,indicating that soil nutrients come from litter and there is a certain coupling relationship between soil nutrients and litter nutrients.(5)The gaps enhance the correlation between the ecological chemometric characteristics of litter and soil in PDS and RPL forests.The P content and C: P of litter were significantly negatively correlated with soil in the gaps of PDS and RPL forests.The C content and N: P of litter in the gaps of RPL forest were significantly positively correlated with soil,respectively.The correlation between the C,P content,C: P,and N: P of litter-soil was stronger in the gaps of PDS and RPL forests.This indicates that forest gaps affect the nutrient distribution patterns and chemometrics characteristics of the ecosystems of PDS and RPL forests,affecting the distribution,transformation,and circulation of nutrients in litter and soil,thereby enhancing the coupling relationship between them.