Fruit production of shrub, Caragana korshinskii, following above-ground partial shoot removal: mechanisms underlying compensation

A number of studies have showed that under some conditions plant may partially, fully or overcompensate for tissue loss, however, the mechanisms underlying compensation are not well understood and still need to be researched. We examined the ability of Caragana korshinskii to compensate for fruit production after above-ground partial shoot removal. Fruit production of 30% main shoot length removal (30% RSL) and 25 and 50% main shoot number removal (25% RSN, 50% RSN) resulted in overcompensation and the response of 60% main shoot length removal (60% RSL) was full compensation. Plants’ responses associated with compensation included (1) greater reproduction efficiency (RA); (2) increased fruit set; (3) decreased fruit abortion; (4) increased seed number per pod; and (5) higher individual seed biomass. These responses may have resulted from more nectar production per flower, more sucrose flux per pod and more sucrose flux per seed of clipped plants, which may in turn have resulted from (1) drawing upon more non-structural carbohydrate (TNC) from roots to supply flower bud development and the flush of new foliage; (2) supplying more photosynthetic assimilation to fruit development owing to increases in leaf-level photosynthetic rates. Increases in leaf-level photosynthetic rates may be caused by more nutrient (nitrogen) and water availability per unit area of resource leaves after clipping.     

Effects of shoot excision on in situ soil and root respiration of wheat and soybean under drought stress

Little information is available about the variability of root-derived respiration rate in relation to biotic factors such as photosynthesis and substrate availability in roots. Here we examine the role of decreased carbohydrates availability on root-derived respiration through removal of above ground biomass. Spring wheat (Triticum aestivum L. cv. Longchun 8139) and soybean (Glycina max L. cv. Tianchan 2) were grown in the field under a moveable rain shelter, and subjected to three different water regimes: (1) well-watered control; (2) moderate drought stress, and (3) severe drought stress. Root-derived respiration before and after shoot clipping, and the concentration of total nonstructural carbohydrate, malic and citric acid were measured for spring wheat and soybean. Root-derived CO₂ flux and total nonstructural carbohydrate concentration of clipped wheat decreased by 38% and 31%, respectively. However, for soybean the root- derived CO₂ flux and total nonstructural carbohydrate concentrations were only 58% and 62% of control, respectively, indicating the root respiration rate was controlled by the availability of carbon in the root. A significant positive correlation between total nonstructural carbohydrate concentration of the root and soil water content was observed in unclipped plants. Total nonstructural carbohydrate contributed 93% of the variance in root-derived respiration. Our results clearly show, that in the field, the availability of carbon substrate in roots determines root-derived respiration and plays a key link between soil moisture and root-derived respiration. A period of time is needed for root respiration to return to “steady-state” after shoot removal and this period needed is strongly dependent on species and soil water content.     

Responses of Caragana korshinskii to different aboveground shoot removal: combining defence and tolerance strategies

BACKGROUND AND AIMS: It is generally assumed that plants respond to natural enemies by either allocating resources to resistance traits or compensating for damage. This study evaluated how different methods of artificial shoot removal influence two alternative strategies (i.e. tolerance and defence) of Caragana korshinskii in the semi-arid area of China. METHODS: Zero per cent (control), 30% (30%) and 60% (60%) of the main shoot length and 25% (25%), 50% (50%) and 100% (100%) of the numbers of main shoots were removed from shrubs. KEY RESULTS: Moderate clipping treatments [30% removal of partial shoot length (RSL), 25% removal of shoot number (RSN) and 50% RSN] improved seed production, whereas the most intensive clipping treatments (60% RSL and 100% RSN) with most or total removal of potential flower buds reduced current reproduction fitness compared with controls. All treatments produced a similar leaf phenolic content, with the exception of 100% RSN which resulted in a low leaf phenolic content. In spite of a substantial investment in regrowth, clipped plants increased biomass allocation to physical defence. Control plants almost did not grow, had lower levels of physical defence and a lower photosynthetic rate, mobilized fewer carbohydrates from roots and produced more flowers. However, their current fitness was lower than that of plants undergoing clipping treatments (30% RSL, 25% RSN and 50% RSN) because of the high level of abortion of flowers and fruits. CONCLUSIONS: Caragana korshinskii responded to aboveground shoot removal through combining defence and tolerance strategies.     

The invasive plant Alternanthera philoxeroides benefits from clonal integration in response to defoliation

Many notorious alien invasive plants have the capacity for vigorous clonal growth, and clonal integration may contribute to their invasiveness in response to various disturbances. Here, it is hypothesized that clonal integration affects the growth, biomass allocation, physiology, and compensatory response of the alien invasive clonal plant Alternanthera philoxeroides when faced with defoliation. To test these hypotheses, a growth experiment was conducted to investigate the effect of clonal integration on the responses of A. philoxeroides to different levels of defoliation. Daughter ramets that had been grown with stolon connections that were either severed from or connected to the mother plant were subjected to four defoliation levels: 0 (control), 30% (mild), 60% (moderate) and 90% (heavy) removal of leaf tissue. Defoliation greatly decreased growth (total biomass, number of ramets and total stolon length) but increased the maximum quantum yield of photosystem II (F_v/F_m) of daughter ramets. Clonal integration significantly increased growth, F_v/F_m and contents of non-structural carbohydrates (soluble sugars and total non-structural carbohydrates) of A. philoxeroides, and these effects were larger under heavier defoliation. Moreover, clonal integration markedly reduced the shoot/root ratio of A. philoxeroides, and these effects tended to increase with increasing levels of defoliation. These results support our hypothesis that A. philoxeroides benefits from clonal integration in response to defoliation, suggesting that clonal integration may be closely related to the invasiveness of A. philoxeroides in natural habitats with frequent disturbances.     

刈割对外来入侵植物黄顶菊的生长、 气体交换和荧光的影响

为明确不同刈割处理对黄顶菊生长和生理特性的影响,本研究在田间条件下,对黄顶菊在生长季内不同时间进行刈割处理。结果表明,刈割降低了黄顶菊植株各部分的生物量积累,其中以刈割3次效果最为显著,使黄顶菊总生物量、根生物量、茎生物量、叶生物量分别较对照下降82.57%、44.53%、80.04%、91.76%;植株的高度和花序数随刈割次数的增加显著降低,其中刈割3次的花序数为0;刈割1次植株分枝数最大,出现超补偿现象,刈割3次分枝数显著低于其他处理;叶绿素含量除了刈割2次出现增高趋势外,随刈割次数的增加,叶绿素含量逐渐降低;刈割处理使黄顶菊净光合速率(Pn)、气孔导度(Cond)和蒸腾速率(Tr)均显著升高;刈割3次的PSⅡ的最大光化学效率(Fv/Fm)和PSⅡ的潜在活性(Fv/F0)显著低于其它各处理,而初始荧光(F0)则显著增加;生长指标的可塑性指数大于生理指标可塑性指数,表明前者在黄顶菊对刈割处理等物理措施适应方面起到了更为重要的作用。总之,刈割3次处理黄顶菊的各项生长和生理指标所受影响最大,对黄顶菊植株的再生和开花结实抑制效果最为理想。     

Effects of endomycorrhizal infection,artificial herbivory,and parental cross on growth of Lotus corniculatus L.

Summary We examined how combinations of parentage, fungicide application, and artificial herbivory influence growth and shoot phosphorus content in pre-reproductive Lotus corniculatus, using young offspring arising from three parental crosses, two of which had one parent in common. Soil with vesicular-arbuscular mycorrhizal (VAM) fungi was treated with either water or benomyl, an anti-VAM fungicide, and added to trays containing groups of four full siblings. There were two experiments; in the first no plants were clipped while in the second two of the four plants were clipped to simulate herbivory. In both experiments plants of the two related crosses accumulated more biomass and total shoot P than did plants of the third cross. Plants inoculated with watertreated soil had greater shoot mass and P concentration than did fungicide-treated replicates but the extent of increase in P concentration varied among crosses. In Experiment 2, clipping reduced root mass and resulted in higher shoot P concentration. In this experiment there was a significant interaction of fungicide application and clipping: both unclipped and clipped plants grew better in soil not treated with fungicide, but the increase in shoot mass, total mass, and total P was greater in unclipped plants. Significant interaction of fungicide treatment and clipping is most likely due to reduced availability of carbon to the roots of clipped plants, resulting in poorer symbiotic functioning.     

Production and rain use efficiency in short-grass steppe: grazing history,defoliation and water resource

Abstract. Grassland in the semiarid shortgrass steppe, subjected to 50 years of heavy, light, and no grazing intensity, was clipped to simulate the natural pattern and intensities of defoliation by cattle or not clipped. A level of water resource treatment was superimposed upon the grazing and clipping treatments. Half of the plots were supplemented with additional water to simulate a wet year and half were not supplemented in a year of average precipitation. All three treatments interactively determined above-ground production. Water treatment had the largest overall effect on above-ground production. Current-year defoliation had no direct significant effect on production, but mediated differences between both longterm grazing and watering treatments. Long-term ungrazed compared to grazed grassland was capable of responding to high amounts of precipitation, but was also most affected by low amounts of precipitation and, therefore, displayed greater variability in above-ground production and rain use efficiency. Only in the year of average precipitation, defoliation increased rain use efficiency in long-term lightly, but not heavily, grazed treatment. This suggests a water conservation mechanism of defoliation that is reduced with heavy grazing.     

Biomass and mineral element responses of a Serengeti short-grass species to nitrogen supply and defoliation: compensation requires a critical [N]

Large mammalian herbivores in grassland ecosystems influence plant growth dynamics in many ways, including the removal of plant biomass and the return of nutrients to the soil. A 10-week growth chamber experiment examined the responses of Sporobolus kentrophyllus from the heavily grazed short-grass plains of Serengeti National Park, Tanzania, to simulated grazing and varying nitrogen nutrition. Plants were subjected to two clipping treatments (clipped and unclipped) and five nitrogen levels (weekly applications at levels equivalent to 0, 1, 5, 10, and 40 g N m⁻²), the highest being equivalent to a urine hit. Tiller and stolon production were measured weekly. Total biomass at harvest was partitioned by plant organ and analyzed for nitrogen and mineral element composition. Tiller and stolon production reached a peak at 3–5 weeks in unclipped plants, then declined drastically, but tiller number increased continually in clipped plants; this differential effect was enhanced at higher N levels. Total plant production increased substantially with N supply, was dominated by aboveground production, and was similar in clipped and unclipped plants, except at high nitrogen levels where clipped plants produced more. Much of the standing biomass of unclipped plants was standing dead and stem; most of the standing biomass of clipped plants was live leaf with clipped plants having significantly more leaf than unclipped plants. However, leaf nitrogen was stimulated by clipping only in plants receiving levels of N application above 1 g N m⁻² which corresponded to a tissue concentration of 2.5% N. Leaf N concentration was lower in unclipped plants and increased with level of N. Aboveground N and mineral concentrations were consistently greater than belowground levels and while clipping commonly promoted aboveground concentrations, it generally diminished those belowground. In general, clipped plants exhibited increased leaf elemental concentrations of K, P, and Mg. Concentrations of B, Ca, K, Mg, and Zn increased with the level of N. No evidence was found that the much greater growth associated with higher N levels diminished the concentration of any other nutrient and that clipping coupled with N fertilization increased the total mineral content available in leaf tissue. The results suggest that plants can (1) compensate for leaf removal, but only when N is above a critical point (tissue [N] 2.8%) and (2) grazing coupled with N fertilization can increase the quality and quantity of tissue available for herbivore removal. Received: 25 August 1997 / Accepted: 14 April 1998     

Manipulating disturbance regimes and seeding to restore mesic Mediterranean grasslands

Question: Can managing disturbance regimes alone or in combination with seeding native species serve to shift the balance from exotic towards native species? Location: Central coast of California, USA. Methods: We measured vegetation composition for 10 yr in a manipulative experiment replicated at three sites. Treatments included no disturbance, grazing and clipping at three frequencies with and without litter removal. We seeded eight native species into clipped plots and compared cover in comparable plots with no seeding. Results: Regardless of frequency, clipping generally shifted community dominance from exotic annual grasses to exotic annual forbs, rather than consistently favoring native species. At one site, perennial grass cover decreased in no‐disturbance plots, but only after 4 yr. Litter removal had minimal impact on litter depth and plant community composition. Grazing had a highly variable effect on the abundance of different plant guilds across sites and years. Seeding increased abundance of only two of eight native species. Conclusions: Managing disturbance regimes alone is insufficient to restore native species guilds in highly‐invaded grasslands and seeding native species has highly variable success.     

手术夹闭与介入栓塞治疗对前交通动脉瘤患者认知功能的影响

目的:探讨前交通动脉瘤手术夹闭与介入栓塞两种治疗方法对前交通动脉瘤患者认知功能的影响。方法:采用简易精神状态量表(MMSE)对206例前交通动脉瘤患者进行分析对照,其中开颅动脉瘤夹闭患者125例,介入栓塞患者81例,另取正常组40例作为对照组。结果:前交通动脉瘤患者术前即有认知功能障碍发生,术后患者认知功能障碍发生率增高(P<0.01)。患者组的术后认知功能障碍发生率明显高于对照组,而患者组中的介入组的术后认知功能障碍发生率明显小于手术夹闭组(P<0.05)。结论:前交通动脉瘤患者术前既有认知功能障碍发生,两种治疗手段对术前即出现的认知功能障碍无改善作用,并且可能增加认知功能障碍的发生率及加重认知功能障碍的程度,而介入栓塞术在认知障碍的发生率及出现认知功能障碍的程度方面都优于开颅动脉瘤夹闭术。