Under global change, the variations of resources such as nutrients and water are not stabilized and often occur in the form of pulses with low frequency, large amplitude, and short duration. The existing evidence suggests that resource pulses have the potential to disrupt the inherent equilibrium of plant communities, and thereby play a critical role in another important component of global change, plant invasion. To date, studies on the impacts of global change on plant invasion have mainly focused on the constant changes of resources, but have ignored the resource fluctuation, in particular the role of resource pulses. Here, we present a literature review concerning the effects of resource pulses on plant invasion, including causes, types and impacts of resource pulses. Then we discuss the importance of resource pulses in plant invasion. Furthermore, our review puts forward some fields that are worthy to be paid more attention in the future, such as the importance of attributes and types of resource pulses, their interactive impacts on and potential mechanisms in plant invasion.

Aims Condensate is an important water source for plants in the ecosystems of drylands. Previous studies have found that some desert plants can absorb condensate via leaves. This study aimed to determine the capacity of the foliar condensate absorption of typical shrub species (Artemisia ordosica and Salix psammophila) in the Mu Us Desert, and to explore the pathways of foliar condensate absorption and transport.

Methods The dehydrated and non-dehydrated detached shoots of A. ordosica and S. psammophilawere placed in an artificial chamber and exposed to deuterium labelled condensate, and the foliar condensate absorption was determined by comparing the differences of shoot masses and isotopic signals between pre- and post-immersion. The potted whole plants of A. ordosica and S. psammophilawere placed in an artificial chamber and exposed to fluorescent tracer solution, and the pathways of foliar water uptake and transport were determined by comparing the differences of fluorescent tracing in leaves and twigs between pre- and post-immersion.

Important findings (1) After the deuterium labelled dew exposure, no significant differences were found in shoot masses between pre- and post-immersion of non-dehydrated detached shoots of A. ordosica and S. psammophila. However, the dehydrated shoot masses significantly increased by 2.04% and 6.74% in A. ordosica and S. psammophila, respectively; the δD (stable isotope ratio of hydrogen) of leaf water increased by 170.10‰ and 104.09‰ in A. ordosica and S. psammophila, respectively; and the δD of xylem water increased by 10.52‰ and 12.72‰ in A. ordosica and S. psammophila, respectively. (2) After the fluorescent tracer solution exposure, fluorescence was observed in the cuticles, stomata, spongy mesophyll, palisade cells and vascular bundle of the leaves of A. ordosica and S. psammophila. The fluorescence was also found in collenchyma of the leaves of A. ordosica. In addition, the fluorescence was observed in phloem, xylem, and pith of twigs of two shrub species. This study found that two typical shrub species in the Mu Us Desert had the capacity to absorb condensate via their leaves, and the plants undergoing water stress had the higher capacity of foliar condensate absorption. The leaves of A. ordosica and S. psammophilaabsorbed condensate through cuticles or stomata, and the absorbed water was transported to vascular bundle and even twigs. Foliar condensate absorption may be an important water use strategy to survive for A. ordosica and S. psammophila during dry periods.

Aims Litterfall is an important component of ecosystem net primary productivity, and a key link between above- and below-ground carbon processes. However, it remains unclear how biodiversity, stand factors and functional traits work together in affecting litterfall production and its temporal stability during forest succession.

Methods We measured litterfall production for three years in plots from four successional stages of broad-leaf and Korean pine (Pinus koraiensis) mixed forests, at the northern limit of Korean pine forest in the Shengshan Reserve of Heilongjiang. Functional traits (leaf carbon and nitrogen contents, specific leaf area) were measured to quantify functional diversity and community weighted mean (CWM) of traits. Tree diameter and height, total basal area (TBA) and gap fraction were measured to quantify stand structure. We used hierarchy partitioning analysis and variance partitioning to evaluate the relative effects of stand factors, community level traits, and (species, functional and phylogenetic) diversity on annual litterfall production, and its temporal stability (= 1/coefficient of variation for annual litterfall production).

Important findings Litterfall production was significantly lower in the early successional stage, but did no vary from the middle to late successional stages. The litterfall stability increased continuously with forest succession. The variable importance of multivariate models also suggest that, the litterfall production was mainly affected by stand factors (e.g. height, TBA, gap fraction) and functional traits (leaf carbon content), with species richness also playing a role. For stability of litterfall production, however, functional diversity was the strongest predictor, followed by stand factors (such as maximum tree diameter). The independent effect of biodiversity on litterfall production was only 0.41%, but was as much higher (33.12%) for temporal stability of litterfall, suggesting that biodiversity have an important influence on litterfall stability that is independent of stand factors and traits. There was also a strong joint effect (up to 53.8%) among the stand factors, biodiversity and functional traits, indicating that these factors collectively affect litterfall production and its stability. Our results suggest that forest succession not only increases forest productivity but also improves ecosystem stability. Therefore, protecting primary forests and promoting forest restoration are effective ways to improve ecosystem functions.

Aims It is very important to investigate the relationships between litter decomposition characteristics and plant functional traits in understanding the maintenance mechanism of ecosystem functions.

Methods In order to study the main driving factors that affect the leaf litters and root decomposition of different species, this study took the leaf litters and roots of six main plant species Stipa grandis, Cleistogenes squarrosa, Anemarrhena asphodeloides, Leymus chinensis, Convolvulus ammannii and Carex korshinskyi in S. grandis steppe. The litter bag method was used to study the decomposition rate constant of both leaf litters and root through 501 days of field incubation. Plant functional traits including leaf dry matter content, root specific surface area, root tissue density, contents of C, N and different cellulose components of the leaf and root litters were determined and the relationships between decomposition characteristics and functional traits of leaf litters and root across six plant species were examined.

Important findingsThe results showed that there were significant interspecific differences in leaf and root traits of six plant species. The ratios of maximum to minimum values for most traits were between 1 and 2, while the difference in some traits, such as C:N and specific surface area of roots between species was nearly 4 times. For the six plant species, the overall trend of the mass residue and decomposition rate constant of the leaf litter and root during 501 days of decomposition all showed the rapid decomposition in the early stage, relatively slow decomposition in the middle stage and the slowest decomposition in the later stage. During the decomposition process of leaf litters and roots, Cleistogenes squarrosa showed the slowest one, while the leaf litter decomposition of Anemarrhena asphodeloides was the fastest, and the root decomposition of Convolvulus ammannii was the fastest. Through the correlation analysis and stepwise regression analysis, it was found that the decomposition process of leaf litters and roots was affected by different traits in different decomposition periods. The structural carbohydrate content was the main factor affecting the early and late decomposition of litters and the early decomposition of roots, while the non-structural carbohydrate content was the main factor affecting the middle and late decomposition of roots. In addition, the decomposition rate of leaf litters in the middle stage of decomposition was mainly affected by leaf dry matter content, while the decomposition rates of roots in the middle and late stages of decomposition were also significantly affected by C:N and N content, respectively. Our results present the important guide for the prediction of carbon and nutrient cycling process in the S. grandis steppe.

Aims This study was conducted to illustrate the spatial heterogeneity of vegetation ecological quality change, and to clarify the driving forces of ecological quality change in Qinling Mountains region from 2000 to 2019.

Methods The methods of model simulation and satellite observation were used.

Important findings The results showed that (1) Vegetation ecological quality in Qinling Mountains region was significantly improved, and the average increase rates of net primary productivity (NPP) and vegetation fractional coverage (VFC) were 8 g C·m^-2·a^-1 and 0.005 4·a^-1, respectively. Spatially, 85%-95% of the Qinling Mountains region showed a significant improvement in ecosystem quality, but NPP and VFC decreased significantly in some areas such as Xiʼan City. (2) 80%-85% of the Qinling Mountains region showed an increasing trend in precipitation and temperature, which was consistent with the distribution area increasing NPP and VFC. These evidence confirmed that warm and humid climate played an important role in improving vegetation ecological quality. (3) Human protection activities (Natural Forest Protection, Grain for Green Project, etc.) have increased the area of woodland, grassland and water area significantly, and a large range of vegetation ecosystems have been nurtured in the Qinling Mountains region. The expansion of construction land represented by the northern slope of Qinling Mountains was the main reason for the deterioration of vegetation ecological quality. However, human destructive activities were limited to local areas.

Aims The occurrence of extreme climate events is becoming more frequent worldwide because of the global warming. This study investigated the responses of vegetation to climate extremes in southwestern China, in order to assess the regional eco-security of natural ecosystems related to global climate change.

Methods The normalized difference vegetation index (NDVI) data from the GIMMS V1.0 datasets with a resolution of 0.083° × 0.083° for the period of January 1982 to December 2015 were used in this study for analysis of the spatiotemporal dynamics of vegetation in the study region. The grid data of regional meteorological variables from the CN05.1 for the period of January 1961 to December 2016 were used to develop the overall climate extreme variables, and the values matching the data period of NDVI were eventually adopted in the analysis on the interrelationships between NDVI and the climate extremes using Pettitt test and trend analysis both before and after detrending.

Important findings Results show that in the study region, NDVI generally increased from 1982 to 2015, with occurrence of an abrupt change in 1994. Prior to 1994, the change in NDVI was not significant, but the increase became significant from this point onward. Before data detrending, only the maximum 1-day precipitation was significantly and positively correlated with NDVI in the precipitation-extremes during 1982-2015. The temperature- extreme variables were all significantly correlated with NDVI except the diel air temperature range. From 1994 to 2015, the maximum 1-day precipitation was significantly and positively correlated with NDVI and the number of wet days was significantly and negatively correlated with NDVI. none of the precipitation-extreme variables was significantly correlated with NDVI. The yearly maximum value of daily minimum air temperature, warm days, summer days, length of growing season and diel air temperature range were all significantly and positively correlated with NDVI, but the cool days, frost days, cool nights and icing days were significantly and negatively correlated with NDVI. During 1982-2015, the NDVI was more strongly correlated with annual mean air temperature than with any of the temperature-extreme variables; whereas during 1994-2015, NDVI was more strongly correlated with summer days and diel air temperature range than with annual mean air temperature. After eliminating the trend, there was no significant correlation between the precipitation-extreme variables and NDVI, but the yearly maximum value of daily maximum air temperature, warm days, summer days and diel temperature range were significantly and positively correlated with NDVI for the entire period of 1982-2015 as well as for the period 1994-2015. The response of NDVI to extreme warm events was more pronounced during 1994-2015 than during 1982-2015, with the strongest correlation between diel air temperature range and NDVI. There was a significant and negative correlation between cool days and NDVI for the period 1982-2015.

Aims The riparian forests in the upper reaches of the Yellow River are typically fragile ecologically. However, the frequent extreme hydrological events induced by climate warming may pose increasing threats to ecological stability and security of this fragile ecosystem type. The ecological resilience and adaptation of riparian forests to extreme hydrological events are of key considerations in eco-environmental management of river basins. This paper aims to determine how Tamarix austromongolica, a major tree species in riparian forests of the upper Yellow River basin, responds to extreme drought and flood and explain the resistance and morphology of these riparian plants against environmental stresses.

Methods We selected 47 Tamarix austromongolica trees from three sampling sites along the upper reaches of the Yellow River. Two mutually perpendicular cores were taken from the trunk of the each sampling tree for estimation of the past annual growth, one from the direction facing the slope and the other along the contour of the nearby mountain. We compared the tree-ring growth between cores from the two sides and grouped them according to whether the growth was strongly affected by geohazards. We analyzed the resistance of the two groups to extreme hydrological events during the past 63 years. The statistical growth difference between two sampling directions from each group was performed by using paired test.

Important findings Tamarix austromongolica trees were found to be very resistant to extreme drought events. The diverse sources of water in riparian zones attributed to their stable growth, which helps enhance their tolerance to hydrological drought events. But the trees injured by geohazards appeared to be more severely affected by droughts. The legacy effect in trauma-associated recovery might initiate high sensitivity to interferences. Moreover, T. austromongolica trees are adapted to a wide range of water conditions and their growth did not appear to be substantially affected by flooding. Well-watered condition along with fully hydrated shoots could promote the growth and counteract the potentially negative effects of submergence in T. austromongolica. However, flood induced geohazards, such as mudslides, could have significantly different impacts on growth in different directions, such that the side facing the nearby mountain slope suffered more growth suppression. These processes could lead to modification of morphology. Studying the growth response of T. austromongolica to extreme drought and flood on the upper reaches of the Yellow River will help assess the ecological resilience of ecologically fragile areas and provide a scientific basis for ecological construction and restoration in riparian zones on the Qingzang Plateau.

Aims Water is essential for plant survival and growth. Water availability affects the anatomical structure and hydraulic function of xylem, and finally makes trees form specific acclimating characters. Therefore, comparing the differences of hydraulic function and anatomical structure between plants growing in field and garden habitats, can facilitate a better understanding on the acclimation of plants to water conditions.

Methods We compared hydraulic safety (water potential at 50% loss of conductivity, P₅₀), hydraulic efficiency (specific hydraulic conductivity, K_s) and xylem anatomy (vessel diameter (D), double thickness of vessel wall (T), vessel density (N), xylem density (WD) and thickness-to-span ratio of vessels ((t/b)²)), between field and garden plants of Acer buergerianum, Cyclobalanopsis glauca and Ligustrum lucidum. We also analyzed the differences of the relationship between xylem hydraulic function and anatomical structure in field and garden habitats.

Important findings We found that: 1) The K_s was higher and P₅₀ was lower in field habitat of the three angiosperms, which were related to the larger D and smaller (t/b)². 2) The intraspecific correlation analysis between K_s and P₅₀ showed that there were no efficiency-safety trade-offs. 3) Intraspecific correlation analysis of anatomical structure and functional traits showed that there was no significant correlation between D and P₅₀; except for L. lucidum in garden habitat, the T and (t/b)²of the other trees was positively correlated with P₅₀. Comparing to garden habitat, plants in field habitat with low water availability or no additional irrigation increased their diameter of vessels to improve water transport efficiency, so as to avoid the decrease of water potential and effectively reduce the potential risk of embolism.

Aims Hydraulic failure is one of the primary cause of plant mortality during drought. Thus, quantitative analysis on inter-specific and inter-organ variance in hydraulic traits can help us to predict the response and even survivability of species under climate change.

Methods Here, three Podocarpaceae species (Podocarpus macrophyllus, P. macrophyllusvar. maki and Nageia nagi) grown in a mesic common garden were studied, with xylem hydraulic function (specific hydraulic conductivity (K_s); embolism resistance (P₅₀)), anatomical structure (tracheid diameter (D_t); hydraulic diameter (D_h); tracheid wall thickness (T_w); tracheid density (N_t); pit membrane diameter (D_p); pit density (N_p)) and mechanical strength (wood density (WD); tracheid thickness to span ratio ((t/b)²)) measured. Then, we analyzed hydraulic traits variance at the organ level (stem and root) in three Podocarpaceae species, and investigated the relationships among xylem hydraulic traits, anatomical structure and mechanical strength in stems and roots.

Important findings We found that: 1) The stem xylem in three Podocarpaceae species exhibited no safety- efficiency trade-off. In contrast, the root xylem exhibited safety-efficiency trade-off. 2) For stems, K_s was positively correlated with D_p, but decoupled with stem WD and (t/b)²; Stem P₅₀ was negatively correlated with D_p, but not correlated with WD and (t/b)². 3) For roots, K_s was positively correlated with hydraulic diameter, but negatively correlated with root T_w and (t/b)²; Root P₅₀ was positively correlated with T_w, (t/b)² and WD. Root xylem traits exhibited strong relationships with both K_s and P₅₀, demonstrating its cause-and-effect basis for the safety-efficiency tradeoff. On the other hand, the absence of safety-efficiency tradeoff in stems may be attributed to the overbuilt xylem of Podocarpaceae. More experimental evidence on the overbuilding of xylem is desired in the future study.

The central Guizhou Plateau is located in the center of the karst region of southwestern China. The typical vegetation type is karst mixed evergreen and deciduous broad-leaved forests on this distinct landform. Due to human disturbances, the main existing vegetation is secondary vegetation in this region. Based on the primary plot-level data obtained from fieldwork during the growing season from 2007-2020, we systematically studied the community characteristics and the classification of these karst forests. The results showed that the typical karst forests are co-dominated by evergreen trees (e.g., Cyclobalanopsis, Itea, Lithocarpus, Machilus and Cinnamomum species) and deciduous trees (e.g., Platycarya, Carpinus, Celtis and Quercus species). Moreover, 585 vascular plants belonging to 318 genera and 124 families were recorded in the 86 forest plots, among which there were 65 ferns species belonging to 27 genera and 11 families, and 520 angiosperm species belonging to 291 genera and 113 families. The karst forests show high diversities of species composition and community type. Based on the dominance principle, these karst forests were classified into 11 alliance groups, 44 alliances and 83 associations.