Response to stem bending in forest shrubs: stem or shoot reorientation and shoot release

Shrubs in the forest understory may be bent by their own weight or by overstory debris. To maintain height growth they must respond to bending by vertical growth of new shoots, reorientation of older axes, or by releasing preventitious buds to form epicormic shoots. I tested for these responses in Ilex verticillata L., Cornus amomum Mill., Gaylussacia baccata (Wang.) K. Koch, Viburnum cassinoides L., Hamamelis virginiana L., and Kalmia latifolia L. For each species, I removed potentially supporting vegetation adjacent to 20 stems, left 10 stems untreated to test for bending by self weight, and bent the remaining 10 stems to 45° to simulate effects of fallen debris. Stem angles and curvatures were measured from before leaf out until just before leaf fall to detect either sagging from self weight or upward bending from tension wood action. Control stems initially leaned out of vertical and five of six species sagged further into a cantilever form. Several control stems failed and bent to the ground. Stems of H. virginiana, I. verticillata, and C. amomum formed tension wood, but only the first two species bent upward. Viburnum cassinoides, G. baccata, and K. latifolia formed no tension wood and sagged further down after being bent. Epicormic shoots formed with varying frequencies in all species except K. latifolia. Epicormic shoots were the major response in C. amomum, V. cassinoides, and G. baccata. New terminal shoots on bent stems recovered toward vertical in I. verticillata and K. latifolia. Negative gravitropic response of shoots was the only recovery mechanism for K. latifolia. Key words: forest shrubs, tension wood, epicormic shoots, bending, stem architecture.

Raw Paper Mill Sludge in A Rooting Medium for Deciduous Woody Cuttings

Stem cuttings of seven deciduous landscape shrubs {silky dogwood (Cornus amomum Mill.), coralberry (Symphoricarpos orbiculatus Moench), Peegee hydrangea (Hydrangea paniculata Siebold. `Grandiflora'), Bridal-wreath spirea [Spiraea ×vanhoutteii (C. Briot) Zab.], spirea (Spiraea ×bumalda Burv. `Goldmound'), fragrant viburnum (Viburnum farreri Stearn), and weigela [Weigela florida (Bunge) A. DC. `Variegata Nana']} were rooted under mist in 100% perlite (no sludge) medium or in mixtures of 10%, 20%, 30%, 40%, 50%, or 60% (v/v) of raw paper mill sludge and perlite. There was a large linear reduction in percent rooting of viburnum (from 80% to 21% with 0% and 60% sludge, respectively) in response to increasing level of sludge. The mean root count per cutting also was significantly decreased, from 14 to 5. However, the length of longest root was unaffected. In contrast, all the other species ranked good to excellent in rooting, regardless of the level of sludge. Differences, if any, in rooting performance were not of practical significance.

Nitrate Loading to the Soil Profile Underlying Two Containerized Nursery Crops Supplied Controlled Release Fertilizer

Cornus amomum and Rhododendron ‘Cary's Red’ were grown in #3 (10 1) containers outdoors and supplied with a controlled release fertilizer (CRF). At two week intervals, core samples were removed from the soil underlying the crop at 30 cm (12 in) increments to a depth of 90 cm (36 in). Soil samples and foliar samples were analyzed for nitrate nitrogen (NO3-N) concentration. NO3-N accumulated rapidly in the upper 30 cm (12 in) of soil underlying containerized crops. Accumulation in the 30–60 cm (12–24 in) layer occurred later in the growing season and NO3-N buildup in the 60–90 cm (24–36 in) layer lagged behind both upper soil layers. Maximum NO3-N concentrations exceeded 40 mg/kg (6.36 × 10−4 oz lb−1) of soil and levels above 20 mg/kg (3.18 × 10−4 oz/lb) of soil were sustained throughout the 90 cm (36 in) soil profile for much of the growing season. Patterns of soil NO3-N concentration suggest that, by the middle of the growing season, rapid-growing Cornus may better utilize released N fertilizer than slower growing Rhododendron. Foliar samples confirm significantly higher NO3-N uptake by Cornus than by Rhododendron.

Pulp composition and the invasion and decay of fruits by microbes

Among temperate-zone plant species, fruits with fat-rich pulp have been predicted to disappear more rapidly than low-fat fruits, in part because of more rapid decay by microbes. The influence of fat content of pulp on the susceptibility of fruits to microbial invasion and the rate of pulp deterioration after invasion were examined using Cornus amomum fruits (approximately 5.8% crude fat) and C. racemosa fruits (approximately 23.1% crude fat). Fruits were surface sterilized, punctured with a sterile needle or left undamaged, and inoculated with sterile water, a suspension of bacteria, or a suspension of fungal spores. The two species did not differ significantly in the number of days to first deterioration (= susceptibility), but whole C amomum fruits deteriorated faster than did whole C. racemosa fruits after invasion was first visible. This difference between species persisted when the difference in mean dry pulp mass was taken into account using an exponential model of pulp decay. The two Cornus species did not differ in rate of pulp deterioration (milligrams dry tissue per day) when a linear model of microbial decay of pulp was used. In these two species, higher fat content of pulp does not yield greater susceptibility to invasion or higher rate of deterioration by microbes.