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Juglans regia L. is a good host for Serendipita indica. Under drought condition, seedlings colonized with S. indica showed higher values in plant height, total fresh biomass, root/shoot ratio, relative growth rate, leaf relative water content and chlorophyll content, gas exchange parameters, maximal photochemical efficiency, photochemical quenching, and effective photosystem II quantum yield than the uncolonized seedlings. It suggested beneficial effects of S. indica on host plants' growth and physiological parameters in response to drought. In comparison with the uncolonized seedlings, S. indica-colonized seedlings showed lower levels in hydrogen peroxide, superoxide anion, malondialdehyde, and relative electrical conductivity under drought condition, suggesting the ability of S. indica to prevent or retard the accumulation of reactive oxygen species and to diminish the oxidative injure. Furthermore, walnut seedlings responded to drought by actively accumulating osmotic regulation substances including soluble protein, soluble sugar, and proline. Root colonization with S. indica was more conductive to the accumulation. Moreover, in response to drought stress, walnut seedlings, regardless of colonization, increased activities of superoxide dismutase, catalase, peroxidase, ascorbate peroxidase, dehydroascorbate reductase, monodehydroascorbate reductase, and glutathione reductase, levels of ascorbate and glutathione, and ratios of reduced ascorbate/dehydroascorbic acid and reduced glutathione/oxidized glutathione in leaves and roots. S. indica colonization induced much more increase in the abovementioned indicators as compared to the uncolonized seedlings. Overall, S. indica colonization alleviated the detrimental effects of drought stress by altering root system, enhancing osmotic adjustment, and repressing the accumulation of reactive oxygen species via stimulating antioxidant system including enzymatic and nonenzymatic components. KEY POINTS: • S. indica stimulated root growth of walnut seedlings under drought condition. • S. indica accelerated osmotic adjustment under drought condition. • S. indica activated antioxidant defense mechanism under drought condition.

Comparative evaluations were conducted to assess the effects of different pH levels, NaCl-induced salt stress, and PEG-induced drought stress on the mycelial growth of Xerocomus badius. The results showed that X. badius mycelium grew well at a wide pH range of 5.00 ~ 9.00. Although the mycelium remained viable, mycelial growth of X. badius was significantly inhibited with increasing salt and drought stresses. Furthermore, a soilless experiment in Petri dishes was performed to investigate the potential of X. badius to induce beneficial effects on seed germination and seedling growth of annual ryegrass (Lolium multiflorum Lam.) under salt and drought stresses. Seed priming with X. badius enhanced the seedling growth of L. multiflorum Lam. under NaCl-induced salt stress and PEG-induced drought stress. However, X. badius did not significantly improve the seed germination under non-stress and mild stress conditions. It suggested that X. badius inoculation with seeds was not essential for seed germination under non-stress and mild stress conditions, but contributed highly to seedling growth under severe stress conditions. Therefore, seed priming with X. badius on ryegrass could be an effective approach to enhance plant tolerance against drought and salt stresses. X. badius could be a good candidate for the inoculation of ectomycorrhizal plants cultivation programs in mild saline and semiarid areas.

Seedlings of three selected Juglans rootstocks (Juglans mandshurica Maxim, Juglans nigra L. and Juglans regia L. cv. Jizhaomian) were analyzed in terms of growth, water use efficiency (WUE), chlorophyll fluorescence and photosynthetic response to drought stress. Significant differences among seedlings of the three analyzed Juglans rootstocks were observed on performance in response to water deficit. Juglans mandshurica Maxim. and Juglans regia L. cv. Jizhaomian showed larger increase in WUE and smaller reduction in growth rate, chlorophyll fluorescence and gas exchange parameters than Juglans nigra L. under drought-stressed condition. It suggests that Juglans mandshurica Maxim. and Juglans regia L. cv. Jizhaomian are more tolerant to drought stress and more suitable as walnut rootstock in water deficit regions as compared with Juglans nigra L.

Plant growth-promoting rhizobacteria (PGPR) are beneficial bacteria that survive within the range of plant rhizosphere and can promote plant growth. The effects of PGPR in promoting plant growth, activating soil nutrients, reducing fertilizer application, and improving the resistance of plant inducible system have been widely investigated. However, few studies have investigated PGPR as elicitors of tolerance to abiotic stresses, especially drought stress. In this study, the effects of Acinetobacter calcoaceticus X128 on the photosynthetic rate (Pn), stomatal conductance (Gs), intracellular CO2 concentration (Ci), and total chlorophyll content [Chl(a+b)] of Sambucus williamsii Hance seedling leaves under moderate drought stress and drought-rewatering conditions were determined. Compared with those of uninoculated seedlings, the average Pn values during the entire drought stress of inoculated seedlings increased by 12.99%. As the drought duration was lengthened, Ci of uninoculated leaves continued to increase after rapidly declining, whereas Gs continuously decreased. Furthermore, their photosynthetic properties were simultaneously restricted by stomatal and non-stomatal factors. After X128 inoculation, Ci and Gs of S. williamsii Hance leaves continued to decrease, and their photosynthetic properties were mainly restricted by stomatal factors. At the end of the drought stress, water stress reduced [Chl(a + b)] of S. williamsii Hance leaves by 13.49%. However, X128 inoculation decreased this deficit to only 7.39%. After water supply was recovered, Pn, Gs, and [Chl(a+b)] in uninoculated leaves were reduced by 14.23%, 12.02%, and 5.86%, respectively, relative to those under well-watered conditions. However, Ci increased by 6.48%. Compared with those of uninoculated seedlings, Pn, Gs, and [Chl(a+b)] in X128-inoculated seedlings were increased by 9.83%, 9.30%, and 6.85%, respectively. Therefore, the inoculation of X128 under arid environments can mitigate the reduction of chlorophyll, delay the restriction caused by non-stomatal factors to Pn in plant leaves under water stress, and can be more conducive to the recovery of photosynthetic functions of leaves after water supply is recovered.

In this study, a pot experiment was carried out in greenhouse to investigate the potentials of Xerocomus badius and Serendipita indica to penetrate and colonize roots of ryegrass (Lolium multiflorum Lam.) and to induce beneficial effects on seed germination and seedling growth. The results showed that X. badius and S. indica successfully colonized in the root system of L. multiflorum seedlings and the root colonization rate was 72.65% and 88.42%, respectively. By microscopy, the hyphae, chlamydospores and spores produced by S. indica were observed in roots cortex of L. multiflorum seedlings. In comparison with the non-inoculated seedlings, seedlings inoculated with X. badius and S. indica showed significant increase in growth parameters with plant height, basal diameter, biomass accumulation, relative growth rate, leaf relative water content and chlorophyll content. Also, we found that seedlings inoculated with S. indica exhibited a greater growth-promotion as compared with X. badius-inoculated seedlings. No significant influence of the two fungus application has been observed with respect to seed germination. It suggested that well establishments of mutualistic symbiosis between L. multiflorum and X. badius or S. indica were not so essential to seed germination but contributed highly to the survival and growth of the seedlings.

The issue of how to alleviate the negative effects imposed by water stress is an interesting problem. Plant growth-promoting rhizobacteria (PGPR) colonize the rhizosphere of plants and are known to promote the growth of crops. However, there are few studies characterizing the physiological response of plants to drought stress after PGPR inoculation. The aim of this study was to investigate the effectiveness of different PGPRs in arid environments and then investigated the effects of PGPR inoculation under drought stress on the physiological characteristics and growth of North China red elder (Sambucus williamsii) nursery container seedlings. The viable count of different PGPRs under drought stress varies widely, and the drought tolerance of Acinetobacter calcoaceticus X128 was significantly higher than that of other PGPRs. In comparison with non-inoculation, inoculation with X128 in an arid environment significantly increased stomatal conductance and mitigated the inhibition of net photosynthetic rate caused by drought stress; this mitigating effect of inoculation is enhanced as the level of drought stress increases. Relative to non-inoculated seedlings, cytokinin levels in the leaves increased by 91.17% under severe drought stress conditions in inoculated seedlings. However, X128 inoculation decreased this deficit to only 44.54%. Compared with non-inoculated seedlings, the relative water content of inoculated seedlings under severe drought stress increased by 15.06%, however the relative conductivity decreased by 12.48%. Consequently, X128 could increase dry matter accumulation of S. williamsii regardless of watering status, indicative of the greater benefits of PGPR on shoot growth than root. Therefore, inoculation of A. calcoaceticus X128 under drought conditions play a significant role for alleviating the negative effects imposed by water stress and promoting plant growth.

Seedlings of six selected walnut rootstock species were analyzed in terms of seed germination rate (GR) and emergence rate (ER) as well as the seedlings’ morphological and physiological performance. A wide variation, with coefficient of variation (CV) range from 6.47 to 38.45 %, was detected for sixteen traits among the studied species. Plant height (PH), total dry biomass, root/shoot ratio, axial root length, number of lateral root, total leaf area, leaf area ratio and leaf chlorophyll content showed higher variation than the other eight indictors, as manifested by the higher CV that was more than 20.00 %. In comparison with other species, Juglans regia L. cv. Jizhaomian (JRJ) and Juglans regia L. cv. Xiangling (JRX) exhibited significantly higher value in GR, ER, morphological and physiological variables. Positive correlations among most variables representing seedling growth suggested that these parameters can be used to predict each other. According to principal components analysis (PCA), three principal components accounting for 75.905 % of the total variance was extracted. Variables with high discriminating values including GR, ER, PH, specific leaf area and water-holding capacity were identified as the most useful variables for evaluation. Bi-plot and cluster analysis divided the studied species into three groups. The first group including JRJ and JRX that were common walnut (J. regia). species and characterized by high GR, ER, well growth performance and high photosynthetic capacity suggesting strong growth vigour. The second group was consisted of three species (J. hopeiensis Hu., J. mandshurica Maxim. and J. sigllata Dode.) which were characterized by moderate value in the studied variables. The third group included Pterocarya stenoptera C. DC. which characterized by low value in the studied variables suggesting weak growth vigour. It suggested a considerable phenotypical diversity in the six walnut rootstock species that would available to rootstock development programs. Our results would have important implications for the production use of these species as walnut rootstocks that are most appropriate for a certain particular walnut planting regions in China. Also, it is of great importance to exploiting the genetic variability and identifying of superior genotypes for conservation action as well as breeding programs.

The smoke tree (Cotinus coggygria Scop.) is not only an important ornamental tree that changes the color of its leaves in autumn but also maintains red juvenile leaves on vigorous sprouting shoots. To elucidate the process of leaf reddening in the smoke tree, we examined the structure and function of its leaf venation system, anthocyanin levels, leaf water conservation ability in red juvenile leaves and green mature leaves, leaf temperature, stomata conductance and snap strength of petiole. A combination of thermography, image analyses and photosynthetic measuring technology was used to study the facts of leaf reddening of smoke tree. We found that spatial and temporal heterogeneity in the pattern of leaf reddening in the smoke tree illustrates the interaction between internal metabolism and environmental factors. These results indicate that there are periods that show water and energy imbalances at leaf lamina and that this phenomenon is essential to leaf reddening, especially during periods of leaf expanding and leaf shedding. We consistently observed a relationship between high temperatures and leaf reddening, which indicates the latter is a photoprotective response induced by imbalances in water and energy.

Super-absorbent polymer (SAP) is a widely studied cross-linked hydrophilic polymer used as water absorbent material. However, little information is available concerning the effects of SAPs on the growth and nutrient accumulation in forest container seedlings. The present study was conducted to quantify the effects of SAP applied with or without fertilizer on the dry matter and nutrient uptake of Pinus pinaster container seedlings. SAP addition with fertilizer increased dry matter along with increased seedling emergence time. However, no effect was found without fertilizer. Compared with fertilizer only, rapid accumulation time of nitrogen (N) and potassium (K) was 7 days longer resulting from SAP addition. The maximum daily N and K accumulations in the fertilized seedlings increased by 9.31 and 10.44 %, respectively, whereas those of the unfertilized seedlings did not differ significantly. SAP addition had little effect on phosphorous (P) uptake, except for an increase in the maximum daily P accumulation under fertilized conditions. The shoot and root of P. pinaster with SAP had 8.61 and 13.70 % higher yields, respectively, than those that received fertilizer only. Compared with fertilizer only, SAP addition with fertilizer increased the N and K contents by 7.15 and 10.04 %, respectively, whereas the P content did not differ significantly. Under fertilized conditions, N, P, and K uptake increased by 17.17, 10.13, and 20.33 %, respectively, from SAP addition. Hence, SAP could be used as a nutrient absorption enhancer (mainly N and K) in forest container seedlings, aside from being a water absorbent material.

A plantation of 5-year-old poplar Populus × euramericana cv. 'Neva' was used to study the regulatory effects of root pruning on nutrients, photosynthetic characteristics, and water-use efficiency (WUE) of leaves and growth rates of diameter at breast height (DBH; 1.3 m), tree height, and volume. Six root-pruning treatments were conducted with different combinations of intensity (at a distance of six, eight or ten times DBH from the trunk) and orientation (on two or four sides of the trees). Results showed that the N, P, K, photosynthetic rate, transpiration rate, and stomatal conductance of leaves were all significantly decreased by root pruning over the initial period following root pruning (30 days), but increased in the subsequent investigations. The values of the above indexes peaked in 8-2 treatment (i.e., eight times DBH distance on two sides). The leaf WUE in 8-2 treatment, and average growth rates of DBH, tree height and volume, were the highest among all treatments within 3 years of root pruning. The results indicated that the root pruning based on the appropriate selection of intensity and orientation had significant positive effects on leaf nutrients, photosynthesis, and growth of trees in a closed-canopy poplar plantation.

One of the proposed mechanisms through which plant growth-promoting rhizobacteria (PGPR) enhance plant growth is the production of plant growth regulators, especially cytokinin. However, little information is available regarding cytokinin-producing PGPR inoculation on growth and water stress consistence of forest container seedlings under drought condition. This study determined the effects of Bacillus subtilis on hormone concentration, drought resistance, and plant growth under water-stressed conditions. Although no significant difference was observed under well-watered conditions, leaves of inoculated Platycladus orientalis (oriental thuja) seedlings under drought stress had higher relative water content and leaf water potential compared with those of noninoculated ones. Regardless of water supply levels, the root exudates, namely sugars, amino acids and organic acids, significantly increased because of B. subtilis inoculation. Water stress reduced shoot cytokinins by 39.14 %. However, inoculation decreased this deficit to only 10.22 %. The elevated levels of cytokinins in P. orientalis shoot were associated with higher concentration of abscisic acid (ABA). Stomatal conductance was significantly increased by B. subtilis inoculation in well-watered seedlings. However, the promoting effect of cytokinins on stomatal conductance was hampered, possibly by the combined action of elevated cytokinins and ABA. B. subtilis inoculation increased the shoot dry weight of well-watered and drought seedlings by 34.85 and 19.23 %, as well as the root by 15.445 and 13.99 %, respectively. Consequently, the root/shoot ratio significantly decreased, indicative of the greater benefits of PGPR on shoot growth than root. Thus, inoculation of cytokinin-producing PGPR in container seedlings can alleviate the drought stress and interfere with the suppression of shoot growth, showing a real potential to perform as a drought stress inhibitor in arid environments.

The spatial distribution and characteristics of fine roots (< 2 mm in diameter), and rhizosphere soil properties were studied in a mixed planted forest of black locust ( L.) and velvet ash ( Torr.) 27 years after planting in a coastal saline soil of the Yellow River delta, China. The results of fine root analysis showed that the fine roots of both black locust and velvet ash were mainly distributed in the soil layer at 0â20 cm depth and 50â150 cm from trees. The fine root distribution of both species suggests a strategy of avoiding salinity rather than salt âtolerance. The horizontal spread distance of fine roots of velvet ash was evidently longer than that of black locust. The fine root biomass, specific root length, specific root area, specific root volume and root activity were significantly higher for velvet ash in comparison with black locust. The results of soil analysis showed that rhizosphere soil pH of black locust and velvet ash were significantly lower compared with non-rhizosphere soil. The available N content in rhizosphere soil of black locust was higher than that of velvet ash. However, the contents of soluble salt, organic matter, available P and available K in rhizosphere soil of velvet ash were higher than those of black locust. The above results indicated that the differences between black locust and velvet ash in fine root distribution, characteristics and rhizosphere soil properties were the major reasons for that velvet ash showed stronger acclimation responses than black locust to the coastal saline soil.Robinia pseudoacaciaFraxinus velutina

Plant growth-promoting rhizobacteria (PGPR) are important catalysts that regulate the functional properties of agricultural systems. However, there is little information on the effect of PGPR inoculation on the growth and nutrient accumulation of forest container seedlings. This study determined the effects of a growth medium inoculated with PGPR on the nutrient uptake, nutrient accumulation, and growth of Fraxinus americana container seedlings. PGPR inoculation with fertilizer increased the dry matter accumulation of the F. americana aerial parts with delayed seedling emergence time. Under fertilized conditions, the accumulation time of phosphorous (P) and potassium (K) in the F. americana aerial parts was 13 days longer due to PGPR inoculation. PGPR increased the maximum daily P and K accumulations in fertilized seedlings by 9.31 and 10.44 %, respectively, but had little impact on unfertilized ones. Regardless of fertilizer application, the root exudates, namely sugars, amino acids, and organic acids significantly increased because of PGPR inoculation. PGPR inoculation with fertilizer increased the root, shoot, and leaf yields by 19.65, 22.94, and 19.44 %, respectively, as well as the P and K contents by 8.33 and 10.60 %, respectively. Consequently, the N, P, and K uptakes increased by 19.85, 31.97, and 33.95 %, respectively. Hence, PGPR inoculation with fertilizer can be used as a bioenhancer for plant growth and nutrient uptake in forest container seedling nurseries.

The aim of this research was to determine the effects of plant growth-promoting rhizobacteria(PGPR) fertilizer on the biological characteristics,root activity,growth and construction of Cerasus pseudocerasus(Lindl.) G.Don(sweet cherry).To prepare sweet cherry biological-fertilizer(YMF),dominant bacteria YT-3,a type of PGPR,was extracted from rhizosphere soil of C.pseudocerasus trees by keeping green method and radish cotyledon weight increase method.Sweet cherry biological-fertilizer was prepared by compounding YT-3 and decomposed chicken manure(DCM).The effects of YMF,normal biological fertilizer(NMF) and DCM on biological characteristics of C.pseudocerasus rhizosphere soil were studied in Yiyuan sweet cherry orchards.And the effects of YMF,DCM and NMF on the root activity,growth and construction of C.pseudocerasus were also investigated.The results showed that YMF increased the amount of bacteria and total microorganism amount in rhizosphere soil of C.pseudocerasus,but the fungus amount was decreased significantly.However,YMF had no influence on actinomycetes amount in rhizosphere soil.Root activity in YMF was significantly increased by 15.33%,22.49% and 13.25% than that in CK,NMF and DCM,respectively.YMF had great influence on the root growth and construction of C.pseudocerasus.Root weight,especially fine root weight in 0～40 soil profile of YMF was significantly increased.Rhizosphere soil pH value in YMF decreased by 8.61% than that in NMF.In addition,YMF significantly enhanced available phosphorus and potassium contents by 17.21% and 9.56%,respectively,compared to that in NMF.However,it had no effects on available nitrogen content in sweet cherry rhizosphere soil.Moreover,PGPR fertilizer increased the cation exchange capacity of rhizosphere soil,which benefited the nutrient retain and uptake of C.pseudocerasus.As a result,plant growth-promoting rhizobactera biological-fertilizer benefited the ecological environment of sweet cherry rhizosphere soil,improved nutrient availability and cation exchange capacity,increased the root activity and benefited the root growth,especially fine root growth in top soil(mainly 0～40 cm).