Key messageRoot morphology and tensile strength were affected by elevation, with changes in the former showing adaptation to the environment, and changes in the latter mainly influenced by root chemical composition.AbstractPlant roots have absorption and anchorage functions and play important roles in plant growth and slope stability. Root morphology and mechanics are closely related to root function and are influenced by various factors. However, the impact of elevation, which encompasses a range of environmental changes, has not been fully studied. This study aimed to investigate the responses of root morphology and root mechanics to environmental changes associated with elevation and to explore the possible effects of these responses on root reinforcement. We measured the morphological properties (length, diameter, and number), tensile strength, and chemical composition (cellulose, hemicellulose, and lignin contents) of the taproots and first- and second-order roots of Lespedeza bicolor Turcz. grown at three different elevations (986, 1839, and 2716 m). The lengths of both taproots and lateral roots decreased, while the diameter of lateral roots increased with increasing elevation. Additionally, there was a significant increase in root tensile strength as elevation increased, accompanied by an increase in cellulose content and a decrease in lignin content. Root tensile strength correlated positively with cellulose content and negatively with lignin content. The morphological and mechanical properties of L. bicolor roots are significantly influenced by elevation. Roots exhibit adaptive strategies in response to environmental factors such as hydrothermal conditions and soil nutrient availability. Cellulose and lignin have a significant impact on the biomechanical properties of roots. Regarding soil reinforcement, roots at lower elevations exhibit a more advantageous morphology. Conversely, roots at higher elevations possess greater biomass and tensile strength, making them more resistant to soil erosion under extreme environmental conditions.

Freeze-thaw desertification (FTD) as a specific land degeneration form in high elevations is intensifying in alpine meadows due to climate change and human activities. It causes the formation of desertified patches (DPs), and further aggravating alpine meadow patchiness and impairing ecosystem functions such as water conservation, carbon sequestration and biodiversity maintenance. However, the impacts of FTD on the patch pattern, soil properties, and vegetation succession of alpine meadows and the elevation differences of these impacts still lack a comprehensive understanding. Here, we analyzed the patch patterns, soil and vegetation characteristics in typical FTD regions in the Qilian Mountains using aerial photography and field investigations along an elevation gradient. Our results indicated that, as elevation increases, the fragmentation of alpine meadows caused by FTD intensified, which was related to the elevational differentiation of freeze-thaw cycles and soil water holding capacity. DPs not only led to a decrease in soil water holding capacity and an increase in bulk density, but also caused surface soil sandification. Among them, the weakening of soil water holding capacity by DPs was particularly serious in high elevations. Additionally, the degradation of the original vegetation species com-munities in DPs caused the significant loss of vegetation cover, biomass and soil organic carbon, and made DPs exhibit certain alpine desert steppe characteristics, whereas the vegetation diversity of DPs had an increase at low elevations. Our findings highlight the significant impacts of FTD on the water conservation function and vegetation diversity of alpine meadows, and it is necessary to apply ecological protection measures to control DPs expansion such as fenced grazing, biological control and land cover (crop, vegetation, degradable plastic mulch, etc.).

Climate change has significantly impacted vegetation phenology across the globe with vegetation experiencing an advance in the spring green-up phases and a delay in fall senescence. However, some studies from high latitudes and high elevations have instead shown delayed spring phenology, owing to a lack of chilling fulfillment and altered snow cover and photoperiods. Here we use the MODIS satellite-derived view-angle corrected surface reflectance data (MCD43A4) to document the four phenological phases in the high elevations of the Sikkim Himalaya and compared the phenological trends between below-treeline zones and above-treeline zones. This analysis of remotely sensed data for the study period (2001-2017) reveals considerable shifts in the phenology of the Sikkim Himalaya. Advances in the spring start of the season phase (SOS) were more pronounced than delays in the dates for maturity (MAT), senescence (EOS), and advanced dormancy (DOR). The SOS significantly advanced by 21.3 days while the MAT and EOS were delayed by 15.7 days and 6.5 days respectively over the 17-year study period. The DOR showed an advance of 8.2 days over the study period. The region below the treeline showed more pronounced shifts in phenology with respect to an advanced SOS and a delayed EOS and DOR that above treeline. The MAT, however, showed a greater delay in the zone above the treeline than below. Lastly, unlike other studies from high elevations, there is no indication that winter chilling requirements are driving the spring phenology in this region. We discuss four possible explanations for why vegetation phenology in the high elevations of the Eastern Himalaya may exhibit trends independent of chilling requirements and soil moisture due to mediation by snow cover.

Mountain regions are vulnerable to climate change but information about the climate sensitivity of seasonally snow-covered, subalpine ecosystems is still lacking. We investigated the impact of climatic conditions and pedogenesis on the C and N cycling along an elevation gradient under a Larch forest in the northwest (NW) Italian Alps. The environmental gradient that occurs over short distances makes elevation a good proxy for understanding the response of forest soils and nutrient cycling to different climatic conditions. Subalpine forests are located in a sensitive elevation range-the prospected changes in winter precipitation (i.e., shift of snowfalls to higher altitude, reduction of snow cover duration, etc.) could determine strong effects on soil nitrogen and carbon cycling. The work was performed in the western Italian Alps (Long-Term Ecological Research- LTER site Mont Mars, Fontainemore, Aosta Valley Region). Three sites, characterized by similar bedrock lithology and predominance of Larix decidua Mill., were selected along an elevation gradient (1550-1900 m above sea level-a.s.l.). To investigate the effects on soil properties and soil solution C and N forms of changing abiotic factors (e.g., snow cover duration, number of soil freeze/thaw cycles, intensity and duration of soil freezing, etc.) along the elevation gradient, soil profiles were opened in each site and topsoils and soil solutions were periodically collected from 2015 to 2016. The results indicated that the coldest and highest soil (well-developed Podzol) showed the highest content of extractable C and N forms (N-NH4+, DON, DOC, C-micr) compared to lower-elevation Cambisols. The soil solution C and N forms (except N-NO3-) did not show significant differences among the sites. Independently from elevation, the duration of soil freezing, soil volumetric water content, and snow cover duration (in order of importance) were the main abiotic factors driving soil C and N forms, revealing how little changes in these parameters could considerably influence C and N cycling under this subalpine forest stand.