Coppicing affects growth, root:shoot relations and ecophysiology of potted Quercus rubra seedlings

Two experiments were conducted to examine the response of Quercus rubra L. seedlings to coppicing. In a greenhouse experiment, growth, biomass distribution, leaf gas exchange, and water and carbohydrate relations were measured for 1-year-old seedlings that were either coppiced when dormant at the time of planting or left intact as controls. Coppicing induced sprouting from the base of the stem, and, in general, the physiology of sprouts and controls was similar. However, the relative growth rate (RGR) of sprouts was 9% higher than that of controls, allowing sprouts to compensate fully for the initial mass lost to coppicing. In a second experiment, in an outdoor cold frame, growth, biomass distribution, leaf gas exchange and plant water relations were measured on 1-year-old seedlings that were either coppiced at the time of planting (dormant-coppiced), coppiced soon after bud break (active-coppiced) or left intact (controls). Dormant coppicing again had little impact on seedling physiology, and dormant-coppiced plants again compensated for initial mass loss with a higher RGR. In contrast, active-coppiced seedlings did not compensate for initial mass loss, as their RGR did not differ from that of controls. By the tenth week of the study, leaf gas exchange rates of active-coppiced sprouts were higher than those of dormant-coppiced and control seedlings. Active-coppiced sprouts also had a greater soil-to-leaf hydraulic conductivity (expressed on a leaf area basis) and a lower ratio of leaf area to root surface area than did controls. Across treatments, photosynthetic rate and stomatal conductance were positively correlated with soil-to-leaf hydraulic conductivity, and gas exchange rates and hydraulic conductivity were negatively related to leaf:root area ratio. Thus, the removal of actively growing shoots may have altered subsequent leaf gas exchange largely through coppice-induced changes in leaf-root balance.     

Comparative ecophysiological effects of drought on seedlings of the Mediterranean water-saver Pinus halepensis and water-spenders Quercus coccifera and Quercus ilex

Ecophysiological and structural traits of seedlings of the water-saver Pinus halepensis and the water-spenders Quercus coccifera and Q. ilex were studied in response to water stress under greenhouse conditions. Water deficit reduced stomatal conductance (g _s) and, as a consequence, both net CO₂ assimilation (A) and transpiration rate (E) were also reduced. Water stress also emphasized midday down-regulation of the photochemical efficiency (dynamic photoinhibition) reducing quantum yield of noncyclic electron transport (Φ_PSII), photochemical quenching (qP) and photochemical efficiency of the open reaction centres of PSII () and involved an increase of thermal dissipation of excess energy. However, water stress not only induced dynamic photoinhibition but also brought a reduction in F _v/F _m (chronic photoinhibition). Despite the water-saving strategy of P. halepensis that limited net CO₂ assimilation, this species showed a higher photochemical efficiency and lower photoinhibition than Quercus species. This was not the result of a different photochemical quenching but was linked to a higher value of , indicating a less severe photo-inactivation of PSII. Water stress resulted in a loss of pigment content and in an increase of the carotenoids/chlorophyll ratio, antioxidant capacity and the biomass rate allocated to roots as opposed to that assigned to leaves. P. halepensis showed a lower photoinhibition and antioxidant activity than Quercus species due to its lower pigment content and higher proportion of carotenoids allowing P. halepensis to use, in a more effective way, the lesser excess energy absorbed.     

Aphid-induced reduction of shoot and root growth in Douglas-fir seedlings

1. The short‐ and long‐term effects of photosynthate removal by sap‐sucking herbivores on plant growth were examined by experimentally manipulating densities of an aphid Cinara pseudotsugae (Wilson) on 2‐year‐old Douglas‐fir seedlings Pseudotsuga menziesii (Mirb.) Franco under greenhouse conditions. An 18‐week test was conducted to determine short‐term effects. Effects of long‐term aphid feeding were examined by exposing seedlings to aphid feeding for two consecutive growing seasons. A third experiment evaluated the extent of recovery during 1 year following a single season of aphid feeding. At least 35 seedlings were used in each test. 2. Volume and dry weight of both shoots and roots decreased significantly with increasing aphid feeding in all three experiments. 3. The most significant and severe aphid effect was reduced root tissue density, suggesting carbohydrate depletion due to translocation from roots to shoots. 4. There was no sign of recovery, of either root or shoot growth, during the year following one season of feeding. 5. The results of this study indicate that short‐term feeding by aphids can affect plant growth and structure for a relatively long time.     

Annual and seasonal changes in fine root biomass of a Quercus ilex L. forest

The biomass, production and mortality of fine roots (roots with diameter <2.5 mm) were studied in a typical Mediterranean holm oak (Quercus ilex L.) forest in NE Spain using the minirhizotron methodology. A total of 1212 roots were monitored between June of 1994 and March of 1997. Mean annual fine root biomass in the holm oak forest of Prades was 71±8 g m^–2 yr^–1. Mean annual production for the period analysed was 260+11 g m^–2 yr^–1. Mortality was similar to production, with a mean value of 253±3 g m^–2 yr^–1. Seasonal fine root biomass presented a cyclic behaviour, with higher values in autumn and winter and lower in spring and summer. Production was highest in winter, and mortality in spring. In summer, production and mortality values were the lowest for the year. Production values in autumn and spring were very similar. The vertical distribution of fine root biomass decreased with increasing depth except for the top 10–20 cm, where values were lower than immediately below. Production and mortality values were similar between 10 and 50 cm depth. In the 0–10 cm and the 50–60 cm depth intervals, both production and mortality were lower.     

Influence of wind loading on root system development and architecture in oak (Quercus robur L.) seedlings.

The effect of wind loading on seedlings of English oak (Quercus robur L.) was investigated. Instead of using a traditional wind tunnel, an innovative ventilation system was designed. This device was set up in the field and composed of a rotating arm supporting an electrical fan, which emitted an air current similar to that of wind loading. Oaks were sown from seed in a circle around the device. A block of control plants was situated nearby, and was not subjected to artificial wind loading. After 7 months, 16 plants from each treatment were excavated, and root architecture and morphological characteristics measured using a 3D digitiser. The resulting geometrical and topological data were then analysed using AMAPmod software. Results showed that total lateral root number and length in wind stressed plants were over two times greater than that in control trees. However, total lateral root volume did not differ significantly between treatments. In comparing lateral root characters between the two populations, it was found that mean root length, diameter and volume were similar between the two treatments. In trees subjected to wind loading, an accentuated asymmetry of root distribution and mean root length was found between the windward and leeward sides of the root system, with windward roots being significantly more numerous and longer than leeward roots. However, no differences were found when the two sectors perpendicular to the wind direction were compared. Mean tap root length was significantly higher in control samples compared to wind stressed plants, whilst mean diameter was greater in the latter. Wind loading appears to result in increased growth of lateral roots at the expense of the tap root. Development of the lateral root system may therefore ensure better anchorage of young trees subjected to wind loading under certain conditions.     

Effects of periodic flooding and root pruning on Quercus nuttallii seedlings

In the southern United States, much of the emphasis in bottomland restoration is placed on establishing an oak-dominated forest. Artificial regeneration is an alternative for restoration on cleared lands and where a desirable seed source is not present. Currently the standard procedure for seedling preparation is to prune the roots prior to transplanting in the field. It is not fully known what effect(s) root pruning has on transplanted seedlings. In addition, bottomland restoration efforts inherently take place on floodplains. The potential interaction between root pruning and flooding on seedling performance is not known. This study consisted of two separate but related laboratory experiments. The purpose of the first experiment was to quantify the effects of various percentages of root removal and varying soil moisture regimes on transplanted Nuttall oak seedlings (Quercus nuttallii Palmer). Root pruning treatments consisted of removal of roots at 0%, 25% and 75% while soil moisture regime was maintained at non-flooded or periodically flooded conditions. Plant gas exchange, growth, and survival were measured. Root pruning alone had adverse effects on height growth during the first 72 days following transplanting. Periodic flooding also produced adverse effects on stomatal conductance (p = 0.0002), height growth (p = 0.005), and survival (p = 0.02). Photosynthetic data indicated that as pruning intensified in the periodically flooded seedlings, photosynthetic rates decreased. In contrast, as pruning intensified in the non-flooded seedlings, photosynthesis increased. This demonstrated that pruning rate had a varying effect on photosynthesis dependent upon soil moisture condition. Experiment 2 focused on the effects of varying degrees of root pruning on new root formation. The seedlings were grown under laboratory conditions, harvested at 0, 10, 20, and 30 days after treatment initiation, and analyzed for new root formation. Results of Experiment 2 indicated no difference in new root formation, root length, or root biomass due to the pruning treatment. Overall, our results from both experiments indicated that root pruning had no detectable long-term adverse effects on growth and survival of seedlings under drained soil conditions; however, as results from Experiment 1 demonstrated, if seedlings were planted in periodically flooded conditions, root pruning produced adverse effects. Thus, in restoration efforts utilizing Nuttall oak seedlings, the planting strategy and pruning rate should be carefully evaluated based on the knowledge of sites' hydrology. Alternatively, on sites with unpredictable flooding both pruned and unpruned seedlings may be utilized to ensure survival.     

Inoculation and production of container-grown red alder seedlings

Summary The inoculation ofAlnus rubra (red alder) withFrankia sp. can lead to a highly efficient symbiosis. Several factors contribute to the successful establishment of nitrogenfixing nodules: (1) quantity and quality ofFrankia inoculant; (2) time and method of inoculation; (3) nutritional status of the host plant.Frankia isolates were screened for their ability to nodulate and promote plant growth of container-grown red alder. Inoculations were performed on seedlings and seeds. Apparent differences in symbiotic performance could be seen when seeds or seedlings were inoculated. Plants inoculated at planting performed significantly better than those inoculated four weeks later in terms of shoot height, nodule number and shoot dry weight. If inoculation was delayed further, reduction in shoot height, nodule number and shoot dry weight resulted. The effect of fertilizer was also investigated with regard to providing optimal plant growth after inoculation. Plants receiving 1/5 Hoagland's solution minus nitrogen showed maximal plant growth with abundant nodulation. Plants receiving 1/5 Hoagland's solution with nitrogen showed excellent plant growth with significantly reduced nodulation.     

Ectomycorrhizal fungal community of naturally regenerated European larch (Larix decidua) seedlings

An investigation was undertaken to assess the community structure of ectomycorrhizal (ECM) fungi on naturally regenerating European larch (Larix decidua Mill.) seedlings grown under forest conditions. The sites examined were in two managed monoculture larch forests, differentiated by soil chemistry and mature tree density. Morphological and molecular analyses revealed a total of 22 fungal taxa. From detected ECM fungal taxa, 13 were noted at Site I and 13 at Site II. Only four taxa were found in both sites (Russula ochroleuca, Thelephora terrestris, Lactarius tabidus and Paxillus involutus). The most abundant species at Site I (lower mineral concentration, high tree density) was Hydnotrya tulasnei (25.7?%), followed by Pseudotomentella tristis, Tomentella sublilacina and Russula puelaris. At Site II (higher mineral concentration, low tree density) the dominant fungal symbiont of larch seedlings was clearly Wilcoxina mikolae, which accounted for 74?% of mycorrhizal tips. The less abundant species comprised T. terrestris, L. tabidus, Xerocomus pruinatus and R. ochroleuca. The analysis of similarity (ANOSIM) and non-metric multidimensional scaling (NMDS) ordination clearly separated the ECM fungal assemblages in the two sites tested. Because our study sites were differentiated by many factors, it is not easy to distinguish one factor in particular to explain the differences observed between the ECM communities at Sites I and II. The results obtained significantly increase our knowledge about the diversity of the ECM fungi hosted by L. decidua. The large number of ECM fungi detected was the first observation showing these fungi as symbiotic partners of European larch.     

Germination of Quercus ilex and Q. pubescens in a Q. ilex coppice

Quercus ilex L. (holm oak) coppices, widespread around the Mediterranean basin, are probably the result of 5 000 years of prolonged human disturbance of the original Quercus pubescens Willd. (downy oak) forests. Since disturbance has almost ceased in recent years, a question arises as to the development of these coppices: will the Q. pubescens forests return, or will Q. ilex remain the dominant species? To investigate the phenomenon, we analyzed the first stages, i.e. germination of the two species in holm oak coppices. Our experiments show that both species germinated better in coppices than in clearings or clear-cuts. Moreover, Q. pubescens appears to be slightly favored above Q. ilex and it is suggested auto-allelopathy is involved, at least partially inhibiting the germination of Q. ilex.     

Large-Scale Patterns of Quercus ilex, Quercus suber, and Quercus pyrenaica Regeneration in Central-Western Spain

In Central-Western Spain, forests and woodlands composed of Quercus sp. support outstanding levels of biodiversity, but there is increasing concern about their long-term persistence due to a lack of regeneration. We hypothesize that this regenerative lack is operating on a large geographic scale; that there are differences in the abundance of regeneration between three oak species; that oak regeneration is governed mainly by forest management and structure; and that shrubs act as important physical protectors of seedlings and saplings. We analyzed whether densities of oak seedlings and saplings in several size classes were related to stand-structure, understory, and physiographic variables potentially affecting regeneration. Data collected at a regional level (1 km × 1 km grid) by the Spanish Forest Inventory were evaluated from 2,816 plots. Results revealed that regeneration failure was common for all size categories, from small seedlings to large saplings, and for the three oak species studied, especially the evergreens. Of the Quercus ilex, Q. suber, and Q. pyrenaica plots studied, 49%, 62%, and 20% were lacking any small seedlings, and 82%, 96%, and 56% did not have any large saplings, respectively. Regeneration was positively correlated with tree cover and density, especially of small and medium-sized trees, and negatively correlated with the presence of large trees, indicating that regeneration failure is mostly associated with more open, uniform, and/or aged woodlands. Regeneration densities of Q. ilex and Q. suber were positively correlated with all understory variables, suggesting that the presence of pioneer shrubs represent a major safe site for early tree recruitment, independent from specific shrub species.     

Water relations of pine seedlings in relation to root and shoot growth

The effects of water stress on growth and water relations of loblolly and white pine seedlings were studied during series of drying cycles. As mean soil water potential decreased, growth of roots, needles, and buds decreased. Growth of roots during successive severe drying cycles was not uniform, however. A study of needle and root extension showed that of the total growth of roots for 3 7-day drying cycles, only 6% occurred during the third cycle, while needle extension was uniform for the 3 cycles. The difference in response of needles and roots to drying cycles may be attributed primarily to the effect of water stress on the growing region. When subjected to a severe stress, roots matured toward the tip and became dormant, resulting in less growth during subsequent drying cycles. The intercalary growing region of needles, however, was not altered seriously enough by the stress to cause a difference in amount of growth during each drying cycle.

Transpiration of loblolly pine was lower in the second drying cycle than in the first. Needle water potential after rewatering was as high as that of control plants watered daily; root resistance was apparently not important in restricting transpiration during a second drying cycle. Needle diffusion resistance of loblolly pine, measured with a low-resistance diffusion porometer, was slightly higher during the second drying cycle than during the first. In addition, many primary needles were killed during the first period of stress. These factors contributed to the reduction of transpiration during the second drying cycle. Diffusion resistance of Coleus increased and transpiration ceased during the first drying cycle while water potential remained relatively high. After rewatering, both leaf resistance and transpiration returned to the control level, presumably because the stress during the first period of drying was not severe. The diffusion resistances observed for well-watered plants were 30 to 50 sec·cm⁻¹ for loblolly pine, 3 to 5 sec·cm⁻¹ for Coleus, and 4 to 6 sec·cm⁻¹ for tomato. These values agree closely with those reported by other workers.

     

QTL controlling root and shoot traits of maize seedlings under cold stress

The improvement of early vigour is crucial for the adaptation of maize (Zea mays L.) to the climatic conditions of central Europe and the northern Mediterranean, where early sowing is an important strategy for avoiding the effect of summer drought. The objectives of this study were to identify quantitative trait loci (QTL) controlling cold-related traits and to investigate the relationships among them. A set of 168 F_2:4 families of the Lo964 × Lo1016 cross was grown in a sand–vermiculite substrate at 15/13°C (day/night) until the one-leaf stage. Twenty QTL were identified for the four shoot and two seed traits examined. Analysis of root weight and digital measurements of the length and diameter of primary and seminal roots led to the identification of 40 QTL. The operating efficiency of photosystem II (_PSII) was related to seedling dry weight at both the phenotypic and genetic level (r=0.46, two matching loci, respectively) but was not related to root traits. Cluster analysis and QTL association revealed that the different root traits were largely independently inherited and that root lengths and diameters were mostly negatively correlated. The major QTL for root traits detected in an earlier study in hydroponics were confirmed in this study. The length of the primary lateral roots was negatively associated with the germination index (r=–0.38, two matching loci). Therefore, we found a large number of independently inherited loci suitable for the improvement of early seedling growth through better seed vigour and/or a higher rate of photosynthesis.This paper is dedicated to our friend and colleague Alberto Soldati, who passed away unexpectedly.     

Correlated responses of root growth and sugar concentrations to various defoliation treatments and rhythmic shoot growth in oak tree seedlings (Quercus pubescens)

Background and Aims

To understand whether root responses to aerial rhythmic growth and contrasted defoliation treatments can be interpreted under the common frame of carbohydrate availability; root growth was studied in parallel with carbohydrate concentrations in different parts of the root system on oak tree seedlings.

Methods

Quercus pubescens seedlings were submitted to selective defoliation (removal of mature leaves, cotyledons or young developing leaves) at appearance of the second flush and collected 1, 5 or 10 d later for morphological and biochemical measurements. Soluble sugar and starch concentrations were measured in cotyledons and apical and basal root parts.

Key Results

Soluble sugar concentration in the root apices diminished during the expansion of the second aerial flush and increased after the end of aerial growth in control seedlings. Starch concentration in cotyledons regularly decreased. Continuous removal of young leaves did not alter either root growth or apical sugar concentration. Starch storage in basal root segments was increased. After removal of mature leaves (and cotyledons), root growth strongly decreased. Soluble sugar concentration in the root apices drastically decreased and starch reserves in the root basal segments were emptied 5 d after defoliation, illustrating a considerable shortage in carbohydrates. Soluble sugar concentrations recovered 10 d after defoliation, after the end of aerial growth, suggesting a recirculation of sugar. No supplementary recourse to starch in cotyledons was observed.

Conclusions

The parallel between apical sugar concentration and root growth patterns, and the correlations between hexose concentration in root apices and their growth rate, support the hypothesis that the response of root growth to aerial periodic growth and defoliation treatments is largely controlled by carbohydrate availability.     

Exploring the relationships between reflectance and anatomical and biochemical properties in Quercus ilex leaves

Leaf anatomical parameters such as leaf mass per area (LMA) and biochemical composition can be used as indicators of leaf photosynthetic capacity. The aims of this study are to evaluate the potential of reflectance spectroscopy of fresh leaves for assessing and predicting various parameters, anatomical (LMA and tissue thickness) and biochemical (nitrogen concentration). This paper describes results obtained with fresh leaves of holm oak ( Quercus ilex ), an evergreen oak that is widely distributed from mesic to xeric habitats in the Mediterranean. Fresh leaves (560) were collected over 3 yr at six different sites, from the top to the bottom of the canopy. The reflectance of each leaf was obtained within 1 h of sampling with an NIRSystems 6500 spectrophotometer over the range 400–2500 nm. LMA was determined for all samples; biochemical and anatomical measurements were conducted over representative subsample populations of 92 and 87 leaves, respectively. Stepwise regression calibrations and partial least squares (PLS) calibrations were developed and compared with different spectral regions and mathematical treatments. Calibration equations had high coefficients of determination ( r ² ranging from 0.94 for nitrogen to 0.98 for LMA and tissue thickness). The PLS regressions gave better results than stepwise regressions for all parameters studied. Compared with regressions calculated on raw spectral data, calculations on second derivatives of spectra improved results in all cases. The use of scatter corrections also improved results. These results show that visible and near-infra red reflectance can be used for accurately predicting anatomical parameters and the nitrogen concentration of fresh holm oak leaves. The results support the suggestion that high spectral resolution imaging spectrometry can be a useful tool for assessing functional processes in forest ecosystems.     

Growth and shoot: root ratio of seedlings in relation to nutrient availability

The influence of mineral nutrient availability, light intensity and CO₂ on growth and shoot:root ratio in young plants is reviewed. Special emphasis in this evaluation is given to data from laboratory experiments with small Betula pendula plants, in which the concept of steady-state nutrition has been applied.Three distinctly different dry matter allocation patterns were observed when growth was limited by the availability of mineral nutrients: 1, Root growth was favoured when N, P or S were the major growth constraints. 2, The opposite pattern obtained when K, Mg and Mn restricted growth. 3, Shortage of Ca, Fe and Zn had almost no effect on the shoot:root ratio. The light regime had no effect on dry matter allocation except at very low photon flux densities (< 6.5 mol m^-2 day^-1), in which a small decrease in the root fraction was observed. Shortage of CO₂, on the other hand, strongly decreased root development, while an increase of the atmospheric CO₂ concentration had no influence on dry matter partitioning. An increased allocation of dry matter to below-ground parts was associated with an increased amount of starch in the tissues. Depletion of the carbohydrate stores occurred under all conditions in which root development was inhibited. It is concluded that the internal balance between labile nitrogen and carbon in the root and the shoot system determines how dry matter is being partitioned in the plant. The consistency of this statement with literature data and existing models for shoot:root regulation is examined.     

Soil transfers from valley oak (Quercus lobata Nee) stands increase ectomycorrhizal diversity and alter root and shoot growth on valley oak seedlings

 Soils from valley oak (Quercus lobata Nee) riparian areas of the Cosumnes River Nature Conservancy Preserve near Sacramento, California were added to growth medium of valley oak seedlings grown in a greenhouse or in agricultural fields at Cosumnes which probably once supported valley oak trees and are now replanted with native riparian vegetation or allowed to revegetate naturally. Agricultural field soil from the Cosumnes River Preserve was presumed to be low or lacking in ectomycorrhizal inoculum. The study was designed to (1) determine whether valley oak stand soil transfer could cause mycorrhizal infection on valley oak seedlings in an agricultural field and in a greenhouse, (2) describe ectomycorrhizal morphological types formed on valley oak seedlings, and (3) determine whether seedling growth is enhanced more by transfer of natural valley oak stand soil than agricultural field soil. In the field study, transfer of forest soil increased average ectomycorrhizal diversity (2.4 types) more than transfer of agricultural field soil (1.2 types). Valley oak seedlings were responsive to ectomycorrhizal infection in the field study. With increase in mycorrhizal infection there was an increase in shoot growth at the expense of root growth. In the greenhouse study, both percent mycorrhizal infection and mycorrhizal diversity were increased more by transfer of oak forest and woodland soils than agricultural field soil. Eight morphotypes occurred on seedlings in forest and woodland soils but only three morphotypes in agricultural soil. This result strongly suggests that the agricultural field also harbors ectomycorrhizal propagules but forest and woodland soils support a more abundant and diverse ectomycorrhizal flora. Accepted: 17 August 1997     

Invasion of naturally senescing root cortices of cereal and grass seedlings byMicrodochium bolleyi

Summary In glasshouse experiments, invasion of wheat and grass (Dactylis glomerata) seedling roots byMicrodochium bolleyi was strongly correlated with the pattern and rate of natural senescence of the root cortex. The fungus did not enhance cortical senescence and did not damage roots except in a few instances when it invaded and killed their tips.M. bolleyi behaved as a weak parasite, largely restricted to invasion of naturally senescing cortices of cereal and grass roots.