Seedling Response to Simulated Browsing and Reduced Water Availability: Insights for Assisted Migration Plantations

To facilitate forest transition to future climate conditions, managers can use adaptive silvicultural tools, for example the assisted translocation of tree species and genotypes to areas with suitable future climate conditions (i.e., assisted migration). Like traditional plantations, however, assisted migration plantations are at risk of failure because of browsing by ungulate herbivores. The ability of seedlings to tolerate browsing could also be hampered by low water availability, as is expected under climate change. Using a greenhouse experiment with five eastern North American tree species, we evaluated the effects of simulated winter browsing and reduced water availability on the growth (total biomass, shoot:root ratio), survival, and chemical composition (nitrogen, total phenolics, flavonoids) of seedlings. We compared seedlings from three geographic provenances representing three climate analogues, i.e., locations with a current climate similar to the climate predicted at the plantation site at a specific time (here: current, mid-century and end of the century). We hypothesized that seedlings would allocate resources to the system (shoots or roots) affected by the most limiting treatment (simulated browsing or reduced water availability). Additionally, we evaluated whether the combination of treatments would have an additive or non-additive effect on the growth, survival and chemical composition of the seedlings. Quercus rubra seedlings reacted only to the water reduction treatment (changes in biomass and N concentration, dependent on geographic provenance) while Pinus strobus reacted only to the simulated browsing treatment (biomass and chemical composition). We also observed non-additive effects of reduced water availability and simulated browsing on Prunus serotina, Acer saccharum and Thuja occidentalis. In general, shoot:root ratio and investment in chemical defense did not vary in response to treatments. The regrowth response observed in Q. rubra and A. saccharum suggests that these species could tolerate periodic browsing events, even when water availability is reduced. More information is required to understand their long-term tolerance to repeated browsing events and to harsher and more frequent water stress. We highlight the importance of species-specific growth and allocation responses that vary with geographic provenance, which should be considered by managers when planning climate-adapted strategies, such as assisted migration.

Exudation of organic acid anions by tropical grasses in response to low phosphorus availability

It has been suggested that some tropical grasses can acquire phosphorus (P) from hematite and gypsite by exuding organic acid anions (OAs). However, it remains to be determined exactly which OAs could be involved in each case. The objective of this study was to verify the exudation OAs by ruzigrass (Urochloa ruziziensis), palisade grass (U. brizantha), and Guinea grass (Megathyrsus maximus) as a response to P deficiency. The grasses were grown in leachate columns with adequate and deficient P nutrient solutions. The concentration of OAs in the leacheate and root surface, as well as shoot and root dry matter, and P uptake were determined. Citrate, isocitrate, and malate concentration in leachates and root surfaces increased with P starvation, mainly for the Urochloa grasses. Oxalate exudation was similar for the grasses under adequate P supply, but was lower in Guinea grass under P starvation. Palisade grass showed a higher concentration of total OAs in the root surface than the other species due to a great production of oxalate and isocitrate. Palisade grass showed greater dry matter yields regardless of P deficiency, and Guinea grass always had the higher shoot:root ratio. Urochloa grasses have a higher capacity to cope with low P availability by exuding OAs along with a lower shoot:root ratio than Guinea grass.

Variation in seedling budburst phenology and structural traits among southwestern ponderosa pine provenances

We used a common garden study to investigate genetic variation in spring budburst phenology, growth, and structural traits of ponderosa pine (Pinus ponderosa Lawson & C. Lawson var. scopulorum Engelm.) seedlings from 10 provenances of different elevations in Arizona and New Mexico, United States. Seedlings were grown with ample resources for two growing seasons in a greenhouse in northern Arizona. Budburst date was measured at the onset of the second growing season; seedling growth, biomass, biomass ratios (shoot:root ratio, root mass ratio, stem mass ratio, and leaf mass ratio), and specific leaf area were measured at the end of the second season. Low-elevation provenances (<2000 m) had earlier budburst and lower specific leaf area than middle- (2000–2500 m) and high-elevation (>2500 m) provenances. Height, leaf length, biomass, and biomass ratios were similar for elevational groups. Total biomass was positively correlated (r = 0.824) with provenance mean annual precipitation. Shoot:root ratio was positively correlated (r = 0.652) with longitude. Results suggest adaptation of low-elevation provenances to warm spring temperatures (early budburst) and aridity (low specific leaf area), inherently faster growth of provenances from wet locations, and greater allocation to shoots in eastern provenances. Such information about geographic patterns of genetic variation may be useful for selecting seed sources for planting in a changing climate.

Initialism as a mechanism of weed interference: can a crop plant be blinded?

Initialism is a new word proposed to indicate the "shade-avoidance syndrome". Plants detect the presence of neighbor plants very early in the growing season through changes in light quality. They modify the allocation of photosynthesis products privileging shoot growth over the roots. One of the hypotheses of the authors is that, when weed management is timely scheduled, a "blind" crop could be more productive because it would avoid an imbalance on the shoot:root ratio (S:R). Two strategies were developed to test this hypothesis: a) to use the classical Yoda's Law to screen several crops for insensitivity to S:R imbalance; b) to evaluate several growth regulators to control the plant responses to crowding. Experimental results confirm that both strategies can yield insensitive plants. The possibilities of the use of this knowledge are discussed.

Imidazolinone-Tolerant Rice Response to Imazethapyr Application

Greenhouse research was conducted to evaluate shoot and root growth response of imidazolinone-tolerant (IT) rice cultivars to imazethapyr applied postemergence at various rates and application timings. Imazethapyr was applied at 70, 140, and 280 g ai/ha to IT cultivars ‘CL 121’ and ‘CL 161’ in the one- to two-leaf and three- to four-leaf growth stages. Imazethapyr applied to one- to two-leaf or three- to four-leaf rice at 70, 140, and 280 g/ha was more injurious to CL 121 than to CL 161. At 3 wk after treatment (WAT), CL 121 was injured 23 to 38% regardless of application timing. In contrast, CL 161 was injured no more than 11% at 3 WAT. Shoot:root ratio for CL 161 was not affected by imazethapyr application. For CL 121, shoot:root ratio was lower following imazethapyr at 280 g/ha than at 70 or 140 g/ha. Based on shoot fresh weight following imazethapyr at 70 g/ha, CL 161 was 1.8 times more tolerant than CL 121 at 2 WAT and 1.3 times more tolerant at 3 WAT. The IT rice cultivar CL 161 is inherently more tolerant to imazethapyr than is CL 121 based on visual injury and shoot and root growth.

Influence of Container Design on Root Circling, Top Growth, and Post-Transplant Root Growth of Selected Landscape Species

‘Delaware Valley White’ azalea, ‘Green Luster’ holly, ‘Plumosa Compacta Youngstown’ juniper, and ‘Shasta’ viburnum were grown for 1 to 2 years in four container designs: a conventional straight-walled round container, a square container with corner holes, a round container with stepped-pyramid profiles, and a poly bag. Poly bag, square, and stepped-pyramid containers significantly reduced root circling on all species compared to the traditional straight-walled round container. There were no significant differences in root circling among the three designs. Top growth was harvested at the end of 1 and 2 years. Effect of container design on top dry weight was species dependent. Poly bag, square, and stepped-pyramid containers increased top growth by 11 to 23% compared to the straight-walled round container. However, no one design was consistently superior for 2 years compared to the straightwalled round container. In addition, three of four species did not respond to container design l out of 2 years. Plants were transplanted into the landscape after growing for 1 or 2 years in the containers. After 16 weeks in the landscape, ‘Green Luster’ holly initially grown in poly bag, square, and stepped-pyramid containers had greater new root dry weight and smaller shoot (top):root ratios compared to the straight-walled round container. Top and new root dry weight of ‘Shasta’ viburnum were significantly affected by container design. However, the shoot:root ratios were not significantly different compared to the straight-walled round container. In the landscape, container design did not significantly affect top dry weight, new root dry weight or shoot:root ratio of ‘Plumosa Compacta Youngstown’ juniper.

BIRCH SEEDLING RESPONSE TO IRRIGATION FREQUENCY AND A HYDROPHILIC POLYMER AMENDMENT IN A CONTAINER MEDIUM

European birch (Betula pendula Roth) seedlings (1+ 0 plugs) were planted in a container growth medium amended with 0, 1.2, 2.4, or 3.6 kg/m3 of a commercial hydrogel and watered either daily or once every 3 or 5 days. When hydrogel was incorporated in the growth medium, shoot and root dry weights and lea area were reduced by 19, 29 and 18%, respectively, compared to controls. Shoot height, stem diameter and shoot:root ratio were unaffected by hydrogel amendment rate. Compared to seedlings in polymer-amended media, plants growing in medium without hydrogel had significantly lower stomata1 conductance and transpiration on fewer than 25% of the measurement dates. Irrigation frequency significantly affected all plant growth Indices and stomata1 parameters; seedlings irrigated daily grew the most and had the highest stomata1 conductance and transpiration. Although polymer-amended media held more water than the medium without hydrogel at all measured tensions, this moisture was retained in the expanded gel rather than being available for plant uptake at higher tensions. The hydrogel appeared to have little benefit for container production of birch.

Response of Matua prairie grass and Ellett perennial ryegrass to excess soil moisture in sand, silt and clay soils

The response of 'Grasslands Mama' prairie grass to waterlogging on different soil types was determined and compared with that of Ellett perennial ryegrass in a glasshouse pot trial at Massey University. During the waterlogging, rate of leaf extension (mm/tiller/day) of Matna prairie grass plants decreased, senescence rate (mm/tiller/day) increased, shoot:root ratio increased, and percentage of total plant weight as dead material increased, compared with unwaterlogged plants. These responses were more extreme on a clay soil than a sand, and a long rather than a short soak treatment, and generally disappeared on removal of the waterlogging stress. Shoot:root ratio of ryegrass decreased in response to waterlogging, but changes in components of plant dry weight were minor compared with those of Matna prairie grass. Matna is more sensitive to waterlogging than Ellett ryegrass, and Matna must be sown in the correct environment for it to persist and perform. Keywords Matua prairie grass, Ellett ryegrass, waterlogging, soil oxygen, shoot:root ratio, leaf elongation, leaf senescence

Variation in the root mass of ryegrass types and its ecological consequences.

The shoot:root ratio of Italian ryegrass and perennial ryegrass cv. in the vegetative phase was constant under constant conditions. With intermittent N supply, root mass and shoot:root ratio of ryegrass in monoculture varied widely. Both relatively and absolutely, root mass was larger than with constant N supply. Short periods of low N were sufficient for a marked increase in root growth. Under constant environmental conditions root mass was closely related to defoliation frequency. Considerable genetic variation in root mass existed between perennial ryegrass clones. Differences were largest under conditions of max. root growth. Root mass was positively related to competitive ability. (Abstract retrieved from CAB Abstracts by CABI’s permission)