One of the outstanding challenges facing humankind is increasing crop production under various types of severe environmental conditions. Many measures have been taken to adopt molecular and biotechnological approaches that lead to the development of transgenic plants able to deal with such harsh and polluted environments. However, such solutions could be very expensive and require considerable efforts and time to achieve these objectives. The main objective of this review is to discuss the new biological solutions that have emerged in the last decade, as environmentally friendly approaches, perhaps to support and/or replace the present efforts. These solutions based on plant–microbe interactions could be a lifeline and promising alternative strategy to create plants with a high resistance to the extreme environments.

During the last two decades research projects have been conducted to study the ecology, identify the features, and the ecophysiology of native plants and the associated microorganisms in the Arabian Gulf region and particularly in Qatar. Many physiological and biochemical parameters have been determined, including organic solutes (amino acids like proline, glycinebetaine, soluble sugars, etc.), photosynthetic pigments, organic acids and inorganic ions especially heavy metals, along with the physical and chemical properties of the soil in various locations of the State of Qatar. Also, the microorganisms adjacent to and associated with these native plants were identified to elucidate the possible roles in the soil biota in supporting these plants against extreme environmental conditions.

Investigations of native plants in the Arabian Gulf states during the last decade have shown that wild plants exhibit different abilities to accumulate organic solutes to cope with the harsh natural environments. Pollution is a major factor stressing wildlife in this region due to the expansion of urban sectors and industrial activities of oil and gas. Compatible osmolytes, like proline, accumulate in wild plants in response to severe environmental conditions and heavy metal contaminated soil. Accumulation of these solutes in plant tissues could provide some level of adaptation and resistance against all these types of environmental stresses. We present some promising efforts in the Arabian Gulf region to remediate desert soil and water polluted with heavy metals and petroleum hydrocarbons. Substantial evidence is introduced about the roles of microorganisms associated with wild plants in natural habitats, such association may help them cope with the extreme stresses. Possible mechanisms adopted by microorganisms in alleviating the harsh abiotic stresses facing the wild life are discussed, one of which is the promotion of biosynthesis and transport of organic solutes to the plants. Also, the main possibilities of the origin of activities of the accumulation of compatible organic solutes are suggested and the objectives of the future research are discussed.

Nitrogen (N) enrichment caused by human activities threatens biodiversity and alters plant community composition and structure. It has been found that heavy and infrequent N inputs may over-estimate species extinction, but it remains unclear whether plant community structure will equally respond to frequent reactive N enriched conditions.

We independently manipulated the rates and the frequencies of N addition in a temperate steppe, northern China, between 2008 and 2013.

We found that plant community structure changes, measured by ‘Euclidean distance’ involving species richness, composition and productivity, were significantly positively related to increasing N enrichment rates rather than frequencies. Changes in aboveground net primary productivity (ANPP), plant species richness and shifts in dominant species were observed. Community ANPP increased with N enrichment, whereas species richness reduced. The frequency of N enrichment increased species richness but had no impacts on community ANPP and the relative ANPP of the two dominant species, C₃perennial bunchgrass Stipa grandis and C₃ perennial rhizome grass Leymus chinensis. The ANPP and relative ANPP of the two dominant species were significantly negatively correlated with each other. Moreover, changes in the relative ANPP of S. grandis was negatively associated with the changes in community structure. After 5 years’ treatment, direct influence of the frequency of N enrichment on plant community structure was not observed, but the effects of the rate of N enrichment were apparent. Our results suggested that further study in various ecosystems and with long-term and well-controlled comparisons the frequency vs. the rate of N enrichment may still be needed.

Plants use different types of responses such as tolerance and induced defense to mitigate the effects of herbivores. The direction and magnitude of both these plant responses can vary with plant age. However, most studies have focused on aboveground herbivory, whereas important feeding occurs belowground. Here, we tested the hypothesis that plant tolerance and defense following shoot damage or root herbivory depends on plant age.

In order to test our hypothesis, we exposed the perennial grass species Holcus lanatus to defoliation and root nematode inoculation at three growth stages (young, intermediate and old plants), and examined responses of plant traits related to tolerance (regrowth following defoliation) and defense (leaf and root nitrogen and phenolics).

Defoliation overall reduced plant shoot and root biomass as well as foliar concentrations of phenolics regardless of plant age at defoliation. In contrast, defoliation increased foliar N concentrations, but only when defoliation occurred at intermediate and old plant age. Inoculation with root-feeding nematodes reduced root N concentrations after a prolonged period of growth, but only when nematodes had been inoculated when plants were young. The relative shoot regrowth rate of plants increased immediately after defoliation but this was independent of the plant age at which defoliation occurred, i.e. was not stronger in plants that were defoliated at a more advanced age, as hypothesized. Similarly, relative root growth rates increased shortly after defoliation, but this was only observed for plants defoliated when they were young. We conclude that plant responses to aboveground and belowground herbivory in traits related to both defense and tolerance are affected by plant age, but do not generally change with plant age.

The ground level of boreal pine forests consists of a dense layer of ericaceous shrubs, herbs, grasses, mosses and lichens. The primary productivity of this forest floor vegetation is notable but the role the most common ericoid dwarf shrub plant species, Calluna vulgaris, Vaccinium myrtillus and Vaccinium vitis-idaea, play in carbon (C) cycling in these ecosystems is poorly understood. Here, we studied their C dynamics in detail using plants of similar size (age 14–19 months) in a microcosm study.

We determined the full C balances of these dwarf shrubs for the first time and compared them to those of Pinus sylvestris by using long-term biomass accumulation, 13C pulse labelling and CO₂ exchange measurements in a controlled laboratory experiment.

Pinus sylvestris had significantly higher biomass-based C fluxes than dwarf shrubs, both aboveground and belowground, but the dwarf shrubs did not differ in the biomass-based fluxes. We showed that root respiration of the evergreen ericoid dwarf shrubs was sensitive to the aboveground light conditions as belowground respiration was 50–70% higher under light compared with dark conditions. Such light-related differences were not observed for Scots pine. The observed differences in C dynamics are important in estimating the origin of belowground CO₂ fluxes and in evaluating their biological relevance. Our results improve current understanding of CO₂ sources and sinks in boreal ecosystems.

Nocturnal sap flow (E_night) has been observed in a variety of plant species and environmental conditions. In water-limited environments, E_night is important in the regulation of plant water’s physiology. This study was designed to evaluate the way in which E_night (defined as sap flow from 20:30 to 06:00) responded to changes in the atmospheric vapor pressure deficit (VPD) and the soil water content (SWC), and explored its potential physiological significance for different plant species in a semi-arid area.

We selected three shrub species: Vitex negundo L. (VN), Hippophae rhamnoides L. (HR) and Spiraea pubescens Turcz (SP) in the semi-arid Loess Plateau of China. The plots of the three communities dominated by each of three species were on the same hill slope. Half-hourly sap flow density was measured in six to seven sample stems for each species during the main growing season (June to August 2015). VPD, SWC, leaf water potential (Ψ_leaf) and stomatal conductance (G_s) were measured at the same time. Regression analyses were conducted to determine the relationships between E_night, E_day, E_night/E_daily, VPD and SWC at half-hourly and daily time scales, as well as between E_night, E_day and Ψ_leaf.

The mean values of E_night and E_day were higher, but E_night/E_daily values were lower for VN compared to HR and SP. The responses of sap flow density to VPD and SWC varied at different temporal scales. VPD was the dominant factor that affected E_night and E_day at the half-hourly scale for all three species. In contrast, SWC was the key factor that influenced E_day at the daily time scale. The values of E_day and E_night/E_daily correlated negatively with SWC because the effect of SWC was stronger on E_day than on E_night. Although the low fraction of E_night/E_daily (4%–7%) may indicate a minor short-term effect of E_night on the standing water balance, E_night had ecophysiologically significance to the plants. The discrepancy in Ψ_leaf between sunset and the following day’s predawn (ΔΨ) indicated that stem refilling occurred during this period. SP had the higher fraction of recharge water among the three species, as it had the relatively higher value of ΔΨ/E_night. E_night had positive relationship with predawn G_s. The increased G_s facilitated rapid onset of photosynthesis in the early morning. In addition, the positive correlation between E_night and E_day from 06:00 to 10:30 suggested that E_night was beneficial for transpiration in the following morning. The responses of E_nightto VPD and SWC indicated differences in plant adaptation to drought stress, which provides important information for our understanding of the reactions to climate changes among species in semi-arid areas.

Grassland degradation has become a common problem worldwide. Several studies have analyzed the effects of nitrogen (N) addition on plant growth in grasslands, but few have considered its effects on plant growth in degraded grasslands. The aim of this study was to evaluate the effects of N addition on plant growth in grasslands with different levels of degradation in Inner Mongolia, China.

A 2-year field experiment was conducted to evaluate plant growth response to N addition in degraded grasslands on the Inner Mongolian Steppe. Grasslands with four levels of degradation were selected for N-addition treatments (0, 10, 20, 30, 40, 50 g N m?2 year?1).

Aboveground biomass was increased by N fertilization in degraded grasslands, and N addition was significantly related to increased biomass in grasslands with severe degradation. However, N fertilization did not significantly affect belowground biomass. The effects of N addition on foliar nutrient concentrations in the same species differed among grasslands with different degradation levels. There was an inconsistent response to N addition between Sanguisorba officinalis and Vicia sepium in non-degraded grassland. There was a significant positive correlation between foliar N content and aboveground biomass in grasslands with different levels of degradation. Our results indicate that the effects of N addition on plant growth in grasslands differ according to the severity of degradation. We conclude that N fertilization may be an effective management technique for degraded grasslands in this area and may improve forage productivity in the short term.

The Brazilian cerrado occupies land that could be occupied by seasonal forest, given current climatic conditions and their spatial proximity. Soil has been identified as one of the main determinants of cerrado and forest prevalence. We tested whether cerrado and seasonal forest woody floras were assembled by different processes. We postulated that soil nutrient availability would account for differences in the functional and phylogenetic structure of the cerrado and the seasonal forest.

In 100 5 × 5 m plots distributed along cerrado and seasonal forest patches in south-eastern Brazil, we sampled five individuals with a basal diameter ≥3 cm from 127 species and measured seven of their functional traits (plant height, basal area, tortuosity, leaf size, specific leaf area, leaf dry matter content, and leaf toughness). We constructed a phylogenetic tree and calculated the pairwise mean functional-phylogenetic distances (MFPDs), an approach that accounts for functional and phylogenetic information both separately and combined. We also sampled soils to a depth of 5 cm in each plot and had their chemical and physical properties determined. We related the MFPD to soil properties and compared MFPD between cerrado and forest species.

Phylogenetic distances were higher than functional distances in both cerrado and seasonal forest communities, suggesting trait convergence in both environments. Irrespective of the importance given to functional or phylogenetic information, most of the communities in the cerrado and in the seasonal forest fell within the null expectation, implying either that multiple assembly processes can occur simultaneously along the gradient of soil fertility, or that not all important traits were included. MFPD was related to soil nutrient status when only functional distances were considered. In this case, MFPD was lower in the cerrado than in the forest, indicating that soil nutrient availability influenced plant traits, with the low-nutrient soils in the cerrado constraining the range of variation in these traits. We found largely similar sorting mechanisms occurring in the cerrado and in the seasonal forest when we accounted for several important traits simultaneously along the phylogenetic distances. Nevertheless, we also found strong evidence for abiotic environmental filtering in the cerrado and for biotic filtering in the seasonal forest when relating MFPD to soil variables. Despite not being the only ecological force structuring these communities, soil nutrient status plays an important role in maintaining the functional distinctiveness of the two vegetation types.

Hyptis suaveolens (L.) Poit is an important invader of the tropical and sub-tropical regions of the world. In our study, it has been investigated that how does the H. suaveolens invasion regulate plant species diversity across the seasons in the dry tropical grassland. We hypothesized that a shift in soil inorganic-N availability is caused by invasion, and this shift is integral to access the invasion effect on plant diversity.

The study was performed in experimental plots at the Botanical Garden of the Banaras Hindu University (25°16′3.3″ N and 82°59′22.7″ E), Varanasi, Uttar Pradesh, India. Five replicates (each, 2 × 2m) of non-invaded grassland plots (NIG) and five grassland plots invaded with H. suaveolens (IG) were established. These plots were constructed by transplanting indigenous grassland patches from an adjacent native grassland. In the invaded plots, 20 individuals of H. suaveolens were transplanted per plot. After 1 year of establishment, diversity attributes and soil properties were recorded from these plots in three seasons as per standard protocol.

The results indicated that Hyptis invasion negatively affects plant diversity, with relatively higher impact in rainy season as compared to the winter season. IG exhibited lower soil moisture content and temperature than NIG in rainy season, whereas soil ammonium-N, nitrate-N, total inorganic-N, N mineralization registered higher values for IG than NIG in both rainy and winter season. Diversity indices were negatively correlated with soil inorganic-N pool and N mineralization. However, these indices were positively correlated with microbial biomass carbon (MBC), and the correlation coefficient for this relationship was higher for rainy season as compared to winter. Species richness (r = 0.65) and Shannon diversity (r = 0.757) were significantly correlated with the ratio of ammonium-N to nitrate-N. The negative effect of invasion by H. suaveolens on the plant diversity is possibly mediated by the effect of invasion on N mineralization processes (mainly nitrification) and the availability of soil inorganic-N pools. The study indicates that Hyptis invasion has an enormous potential to change the structure and composition of plant communities in the dry tropical grasslands.

Exploring species-genetic diversity correlation (SGDC) is essential for understanding spatial patterns of diversity and the underlying mechanisms. Until now, latitudinal patterns of species diversity (SD) and genetic diversity (GD) were rarely studied simultaneously. As the freezing-tolerance hypothesis predicts a decrease of SD from low to high latitudes and the central-marginal hypothesis predicts a unimodal pattern of GD along latitude, we hypothesized that SD and GD are uncorrelated. We also tested how climatic and edaphic factors affect the correlation between the two levels of biodiversity.

We measured (i) SD (species richness and Simpson’s diversity index) and community dissimilarity of woody plants (63 plots), (ii) GD (allelic richness and expected heterozygosity) and genetic differentiation of a dominant tree species (Euptelea pleiospermum; 678 individuals from 21 populations) using nuclear microsatellite data, and (iii) climatic (annual mean precipitation, annual mean temperature, minimum temperature, maximum temperature, annual relative moisture, solar radiation, photosynthetically active radiation) and edaphic (total C, total N, total P, available P, K, Ca, Mg, Al, Fe, Mn, Ni, Zn, B, Mo, Cu, pH) variables of 21 sites. We conducted both linear and quadratic regression analyses of diversity parameters against latitude. Relationships between SD and GD were tested using Pearson’s correlation. Pearson’s and Spearman’s ρ correlation coefficients were calculated between diversity parameters and environmental variables. We used stepwise multiple regression analysis to identify the significant environmental predictors of SD and GD.

We observed no significant correlation between measures of SD and GD. SD decreases with increasing latitude, which can be partly explained by the freezing-tolerance hypothesis, whereas GD presents a unimodal pattern along the latitudinal gradient, which is consistent with the prediction of the central-marginal hypothesis. The contrasting latitudinal patterns of SD and GD indicate that the two levels of biodiversity do not co-vary in space. Based on both correlation analysis and stepwise multiple regression analysis, SD is only related to climatic variables, whereas GD is mainly related to edaphic variables. Our results show that different geographical and environmental factors affect SD and GD, driving the non-significant correlation between the two fundamental levels of biodiversity. Furthermore, a significantly positive correlation was observed between genetic distance and community dissimilarity, both of which were significantly correlated with geographical distance.

Radial growth in response to climate has been reported in many trees, but the sex-specific responses of tree-ring growth associated with altitude in dioecious trees are still poorly known. This study aims to examine whether (i) there are sex-related responses of tree-ring growth to climate in dioecious trees; (ii) these responses could be changed with altitude elevation.

The tree-ring width and basal area increment (BAI) were measured over the past 30 years (1982–2011), and the sexual differences in relationship between BAI and time span and correlations between ring width and climatic factors were investigated in Populus cathayana trees at two altitude sites (1,450 m and 1,750 m a.s.l.) in Xiaowutai Mountain, Hebei, north China.

The BAI was increased over the past 30 years. Trees at high-altitude sites had significantly lower mean ring width and mean BAI than those trees at low-altitude sites (P < 0.001). In addition, sexual differences in tree-ring growth and its response to climate were more pronounced by altitude elevation. Male trees had a significantly larger mean ring width and mean BAI than did females at high-altitude sites, whereas no significant sexual differences in these traits were detected at low-altitude sites. Female trees were sensitive to previous October–November temperatures at high altitude but to current February and April precipitation at low altitude (P < 0.05), whereas male trees were sensitive to current June temperature at high altitude but to January precipitation at low altitude (P < 0.05). Our results indicated that the responses of tree-ring growth to climate are sex dependent and can be changed with altitude elevation.

Given the importance of resorption in nutrient conservations, nutrient resorption should change with leaf age if resorption depends on nutrient content, and if nutrient content changes with leaf age. However, no study has addressed this issue.

Here, we measured N and P concentrations of needles of different ages in two woody evergreen conifer species—white spruce (Picea glauca Voss.) and balsam fir (Abies balsamea Mill.)—to determine the effects of needle aging on nutrient resorption.

For both species, N and P concentrations were higher in newer needles than in older needles. Nutrient resorption efficiency, i.e. percentage of nutrients resorbed during senescence, also declined significantly with needle age from 73 to 22% in these two evergreen conifer species. The difference in nutrient resorption between old and young needles may be attributed to the size of N and P sink tissues, which is likely to decrease with needle age. These results suggest that needle age affects the extent of N and P resorption in these two evergreen conifer species.

Seagrasses provide a variety of ecosystem goods and services, but they are subjected to frequently anthropogenic disturbances. In this study, we genotyped samples collected from Zostera japonica meadows with dramatic fluctuations in the area in order to understand the distribution of genetic variation within and among populations.

We collected samples from eight extant populations along coastal areas of southern China. Ten polymorphic microsatellites were adopted to genotype the samples. Parameters of genetic diversity and differentiation were calculated with general software.

High levels of genetic diversity were found in the studied populations, suggesting that the effective population size has not decreased significantly, which was supported by no signs of recent bottlenecks. High genetic diversity reflects an important role of sexual seedling recruitment in Z. japonica populations. We found a significant relationship between genetic differentiation and the shortest sea surface distance of populations, suggesting that ocean currents play a critical role in shaping the genetic structure of Z. japonica populations. STRUCTURE software analysis clustered the eight populations into two groups: western and eastern populations separated by the Qiongzhou Strait/Leizhou Peninsula, hinting that there was very limited gene flow through the narrow strait in this marine plant. Four populations had high contribution diversity and, thus, high priority for in situ conservation.