Contribution of leaves of different ages to plant carbon balance as affected by potassium supply and water stress

The carbon balances of whole, 21-d old French bean plants (Phaseolus vulgaris L.) grown in standard nutrient solution (1K) and its modifications without (OK) or surplus (2K) potassium were calculated from the daily photosynthetic carbon inputs of individual leaves, and the daily respiratory carbon losses by individual leaves, stalks and petioles, and roots. Under the three K concentrations, maximum net photosynthetic rates (P_n) were found in the 2nd or in the 3rd trifoliate leaves, maximum respiratory rates (R_d) in the youngest, 4th trifoliate leaves; the P_n/R_d ratio decreased with leaf age. In all leaves of 2K plants, leaf dry masses and thicknesses, P_n, P_n/P_d ratios, and stomatal and intracellular conductances were lower than in OK and IK plants. Daily whole-plant net carbon gain was highest in IK plants, whereas in OK and 2K plants it was 98.0 and 81.3 % of IK, respectively. Similar values were found in the parameters of growth analysis, namely in net assimilation rates and relative growth rates. No differences were found in water potential (Ψ _w ) or water saturation deficit (W_sat) in the OK, 1K and 2K plants sufficiently supplied with water or during wilting and resaturation. The decrease in Ψ_w to −0.97 MPa was associated with a 19.9 %, 31.4 % and 23.4 % decrease in P_n of OK, 1K and 2K plants, respectively, but no effect on R_d was found. In the three variants, the short-time effect of mild water stress was fully reversible.     

Geographic variation of body size in New World anurans: energy and water in a balance

The validity of Bergmann's rule, perhaps the best known ecogeographical rule, has been questioned for ectothermic species. Here, we explore the interspecific version of the rule documenting body size gradients for anurans across the whole New World and evaluating which environmental variables best explain the observed patterns. We assembled a dataset of body sizes for 2761 anuran species of the Western Hemisphere and conducted assemblage‐based and cross‐species analyses that consider the spatial and phylogenetic structure in the data. In accordance with heat and water‐related explanations for body size clines, we found a consistent association of median body size and potential evapotranspiration across the New World. A relevant role of water availability also emerges, suggesting the joint importance of body size for thermoregulation and hydroregulation in anurans. Anurans do not follow a simple Bergmannian pattern of increasing size towards high latitudes. Consistent with previous regional findings, our Hemisphere‐wide analyses detect that the geographic variation in anuran body sizes is highly dependent on a trade‐off between heat and water balance. The observed size‐climate relationships possibly emerge from the interplay between thermoregulatory abilities and the benefits inherent to reduced surface‐to‐volume ratios in larger species, which decrease the rates of evaporative water loss and favour heat retention. Our results also show how temperature becomes important for species that are directly in contact with the substrate and water, like burrowing and terrestrial anurans, while arboreal species exhibit a body size cline linked with potential evapotranspiration.     

Vascular bundle sheath and mesophyll cells modulate leaf water balance in response to chitin

Plants can detect pathogen invasion by sensing microbe‐associated molecular patterns (MAMPs). This sensing process leads to the induction of defense responses. Numerous MAMP mechanisms of action have been described in and outside the guard cells. Here, we describe the effects of chitin, a MAMP found in fungal cell walls and insects, on the cellular osmotic water permeability (P_f) of the leaf vascular bundle‐sheath (BS) and mesophyll cells (MCs), and its subsequent effect on leaf hydraulic conductance (K_leaf). BS is a parenchymatic tissue that tightly encases the vascular system. BS cells (BSCs) have been shown to influence K_leaf through changes in their P_f, for example, after sensing the abiotic stress response‐regulating hormone abscisic acid. It was recently reported that, in Arabidopsis, the chitin receptors‐like kinases, chitin elicitor receptor kinase 1 (CERK1) and LYSINE MOTIF RECEPTOR KINASE 5 (LYK5) are highly expressed in the BS as well as the neighboring mesophyll. Therefore, we studied the possible impact of chitin on these cells. Our results revealed that BSCs and MCs exhibit a sharp decrease in P_f in response to chitin treatment. In addition, xylem‐fed chitin decreased K_leaf and led to stomatal closure. However, Atlyk5 mutant showed none of these responses. Complementing AtLYK5 in the BSCs (using the SCARECROW promoter) resulted in the response to chitin that was similar to that observed in the wild‐type. These results suggest that BS play a role in the perception of apoplastic chitin and in initiating chitin‐triggered immunity.     

Physiological control of water exchange in anurans

Research on water exchange in frogs has historically assumed that blood osmotic potential drives water exchange between a frog and its environment, but here we show that the “seat patch” (the primary site of water exchange in many anurans), or other sites of cutaneous water uptake, act as an anatomic “compartment” with a water potential controlled separately from water potential of the blood, and the water potential of that compartment can be the driver of water exchange between the animal and its environment. We studied six frog species (Xenopus laevis, Rana pipiens, R. catesbeiana, Bufo boreas, Pseudacris cadaverina, and P. regilla) differing in ecological relationships to environmental water. We inferred the water potentials of seat patches from water exchanges by frogs in sucrose solutions ranging in water potential from 0 to 1000‐kPa. Terrestrial and arboreal species had seat patch water potentials that were more negative than the water potentials of more aquatic species, and their seat patch water potentials were similar to the water potential of their blood, but the water potentials of venters of the more aquatic species were different from (and less negative than) the water potentials of their blood. These findings indicate that there are physiological mechanisms among frog species that can be used to control water potential at the sites of cutaneous water uptake, and that some frogs may be able to adjust the hydric conductance of their skin when they are absorbing water from very dilute solutions. Largely unexplored mechanisms involving aquaporins are likely responsible for adjustments in hydric conductance, which in turn, allow control of water potential at sites of cutaneous water uptake among species differing in ecological habit and the observed disequilibrium between sites of cutaneous water uptake and blood water potential in more aquatic species.     

Ontogeny and tissue differentiation of the pelvic girdle and hind limbs of anurans

We present the ontogeny of the integrated musculoskeletal complex that comprises the pelvic girdle and hind limbs of anurans. Our histological data show that the pelvic girdle originates from a single mesenchymatic condensation. The tissue differentiation sequence is cartilage, muscle and tendon. The intrusion of the ischiadic nerve into the limb bud is produced very early in ontogeny. The pre‐cartilage appears in the pre‐motile stage. Therefore, the nerve produces a movement analogous to the ‘embryonic motility’ that would induce the emergence of the pre‐cartilage. The acetabulum is the first of all cavitation processes to form, the second one being the knee. The acetabulum appears before the muscles are mature, although it has been stressed that the muscle contraction maintains joint progenitors committed to their fate. Our data indicate an explosive differentiation of all 11 muscular masses together. We provide three new characters that support the monophyly of Hyloides, Acosmanura and Neobatrachia.     

Malate valves to balance cellular energy supply

In green parts of the plant, during illumination ATP and NAD(P)H act as energy sources that are generated mainly in photosynthesis and respiration, whereas in darkness, glycolysis, respiration and the oxidative pentose-phosphate pathway (OPP) generate the required energy forms. In non-green parts, sugar oxidation in glycolysis, respiration and OPP are the only means of producing energy. For energy-consuming reactions, the delivery of NADPH, NADH, reduced ferredoxin and ATP has to take place at the required rates and in the specific compartments, since the pool sizes of these energy carriers are rather limited and, in general, they are not directly transported across biomembranes. Indirect transport of reducing equivalents can be achieved by malateoxaloacetate shuttles, involving malate dehydrogenase (MDH) for the interconversion. Isoenzymes of MDH are present in each cellular compartment. Chloroplasts contain the redox-controlled NADP-MDH that is only active in the light. In addition, a plastid NAD-MDH that is permanently active and is present in all plastid types has been found. Export of excess NAD(P)H through the malate valves will allow for the continued production of ATP (1) in photosynthesis, and (2) in oxidative phosphorylation. In the latter case, the coupled production of NADH is catalysed by the bispecific NAD(P)-GAPDH (GapAB) in chloroplasts that is active with NAD even in darkness, or by the specific plastid NAD-GAPDH (GapCp) in non-green tissues. When plants are subjected to conditions such as high light, high CO(2), NH(4) (+) nutrition, cold stress, which require changed activities of the enzymes of the malate valves, changed expression levels of the MDH isoforms can be observed. In nodules, the induction of a nodule-specific plastid NAD-MDH indicates the changed requirements for energy supply during N(2) fixation. Furthermore, the induction of glucose 6-phosphate dehydrogenase isoforms by ammonium and of ferredoxin and ferredoxin-NADP reductase by nitrate has been described. All these findings are in line with the assumption that a changed redox state caused by metabolic variability leads to the induction of enzymes involved in redox poise.     

Vascular functioning and the water balance of ripening kiwifruit (Actinidia chinensis) berries

Indirect evidence suggests that water supply to fleshy fruits during the final stages of development occurs through the phloem, with the xylem providing little water, or acting as a pathway for water loss back to the plant. This inference was tested by examining the water balance and vascular functioning of ripening kiwifruit berries (Actinidia chinensis var. chinensis 'Hort16A') exhibiting a pre-harvest 'shrivel' disorder in California, and normal development in New Zealand. Dye labelling and mass balance experiments indicated that the xylem and phloem were both functional and contributed approximately equally to the fruit water supply during this stage of development. The modelled fruit water balance was dominated by transpiration, with net water loss under high vapour pressure deficit (D(a)) conditions in California, but a net gain under cooler New Zealand conditions. Direct measurement of pedicel sap flow under controlled conditions confirmed inward flows in both the phloem and xylem under conditions of both low and high D(a). Phloem flows were required for growth, with gradual recovery after a step increase in D(a). Xylem flows alone were unable to support growth, but did supply transpiration and were responsive to D(a)-induced pressure fluctuations. The results suggest that the shrivel disorder was a consequence of a high fruit transpiration rate, and that the perception of complete loss or reversal of inward xylem flows in ripening fruits should be re-examined.     

Phosphorus uptake suppression in maize seedlings as related to humate supply

The effect of sodium humate on phosphorus uptake by maize seedlings devoid of the endosperm was studied. Short-term experiments have shown that a suppression of phosphate ion absorption occurs under the described conditions in the presence of humate without decreasing the weight of experimental plants. The effect reported is delayed and is enhanced by prolonging the preliminary phase of starvation. It varies with the pH of the medium and reduces under extreme conditions the phosphate release from the root to the medium.     

Influence of nutrient versus water supply on hydraulic architecture and water balance in Pinus taeda

We investigated the hydraulic consequences of a major decrease in root‐to‐leaf area ratio (A_R:A_L) caused by nutrient amendments to 15‐year‐old Pinus taeda L. stands on sandy soil. In theory, such a reduction in A_R:A_L should compromise the trees’ ability to extract water from drying sand. Under equally high soil moisture, canopy stomatal conductance (G_S) of fertilized trees (F) was 50% that of irrigated/fertilized trees (IF), irrigated trees (I), and untreated control trees (C). As predicted from theory, F trees also decreased their stomatal sensitivity to vapour pressure deficit by 50%. The lower G_S in F was associated with 50% reduction in leaf‐specific hydraulic conductance (K_L) compared with other treatments. The lower K_L in F was in turn a result of a higher leaf area per sapwood area and a lower specific conductivity (conducting efficiency) of the plant and its root xylem. The root xylem of F trees was also 50% more resistant to cavitation than the other treatments. A transport model predicted that the lower A_R:A_L in IF trees resulted in a considerably restricted ability to extract water during drought. However, this deficiency was not exposed because irrigation minimized drought. In contrast, the lower A_R:A_L in F trees caused only a limited restriction in water extraction during drought owing to the more cavitation resistant root xylem in this treatment. In both fertilized treatments, approximate safety margins from predicted hydraulic failure were minimal suggesting increased vulnerability to drought‐induced dieback compared with non‐fertilized trees. However, IF trees are likely to be so affected even under a mild drought if irrigation is withheld.     

Comparative anatomy and development of pectoral and pelvic girdles in hylid anurans

The development of the tetrapod pectoral and pelvic girdles is intimately linked to the proximal segments of the fore‐ and hindlimbs. Most studies on girdles are osteological and provide little information about soft elements such as muscles and tendons. Moreover, there are few comparative developmental studies. Comparative data gleaned from cleared‐and‐stained whole mounts and serial histological sections of 10 species of hylid frogs are presented here. Adult skeletal morphology, along with bones, muscles, and connective tissue of both girdles and their association with the proximal portions of the anuran fore‐ and hindlimbs are described. The data suggest that any similarity could be attributable to the constraints of their ball‐and‐socket joints, including incorporation of the girdle and stylopodium into a single developmental module. An ancestral state reconstruction of key structures and developmental episodes reveals that several development events occur at similar stages in different species, thereby preventing heterochronic changes. The medial contact of the halves of the pectoral girdle coincides with the emergence of the forelimbs from the branchial chamber and with the total differentiation of the linkage between the axial skeleton and the girdles. The data suggest that morphogenic activity in the anterior dorsal body region is greater than in the posterior one, reflecting the evolutionary sequence of the development of the two girdles in ancient tetrapods. The data also document the profound differences in the anatomy and development of the pectoral and pelvic girdles, supporting the proposal that the pectoral and pelvic girdles are not serially homologous, as was long presumed.     

The influence of canavanine and related compounds on the water balance system of locusts

In vivo increase in haemolymph volume of canavanine-treated locusts substantiates our previous in vitro findings that canavanine inhibits fluid secretion by locust Malpighian tubules. Furthermore when diuretic hormone is applied in vivo after canavanine treatment haemolymph volume is drastically reduced below levels retained in locusts untreated with canavanine. Again this is in accord with canavanine potentiation of semi-isolated Malpighian tubules and enhanced fluid secretion in vitro. The response is specific to canavanine; compounds similar in structure (arginine, argininic acid, citrulline, canaline, ornithine and homoserine) have no effect on the rate of fluid secreted by Malpighian tubules. Only partial competition is obtained with uridine homoserine.     

Unusual diel pHs in water as related to aquatic vegetation

High diel pHs (% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGabmiwayaara% aaaa!36E2!\[\bar X\] > 9.0) showing little or no fluctuation were observed in several impoundments. This phenomenon was experimentally produced in water that contained only Myriophyllum spicatum or species of filamentous algae. Diel pHs ⩾ 9.0 were produced in the laboratory with as little as 0.2 g/1 of algae or vascular plants. The ability of these plants to cause high diel pHs in water may have evolved in response to competition with phytoplankton for carbon.     

喀斯特地区耕地生态承载力供需平衡

以喀斯特地区耕地生态承载力供需关系作为切入点,采用GIS软件和耕地生态足迹模型,在修正耕地产量因子的基础上构建喀斯特地区耕地生态承载力供需平衡指数,对以喀斯特地貌为主的毕节市2014年耕地生态足迹供需平衡现状进行分析评价。结果显示:(1)毕节市耕地生态足迹供需在空间分布上呈现北部盈余而南部超载的态势;(2)国内生产总值与耕地生态足迹供需平衡指数之间存在负相关关系;(3)耕地生态承载力供需平衡指数与潜在石漠化、轻度石漠化及中度石漠化面积占比之间存在负相关关系,与强度石漠化面积占比存在正相关关系;(4)全市8县(区)中,4个县(区)耕地生态盈余,2个县耕地生态平衡,2个县耕地生态赤字,全市约75.28%的人口生活在耕地生态盈余区和平衡区,24.72%的人口生活在耕地生态赤字区。可为毕节市农业产业结构调整、生态安全预警、区域经济发展及土地利用总体规划编制提供决策依据。