Question

Answer all questions below.  You should give your sources used, and they should be primarily our book/videos/notes.  Feel free to incorporate images into your answers as well!

1. Explain the basic fungi life-cycle, and the different types of reproductive structures seen. How do these reproductive structures divide the groups up into different phyla within Kingdom Fungi?

2. Explain the role of mycorrhizae in the ecosystem

3. Explain the key differences between bryophyte, gymnosperm, and angiosperm reproductive life-cycles.

4. Explain the role of seeds in plant diversity, and how pollinators (animals) are important for the spread of plants as well

Answer 1

Q)Explain the role of mycorrhizae in the ecosystem

INTRODUCTION:

Most land plants form associations with mycorrhizal fungi. Mycorrhizas aremutualistic associations between fungi and plant roots. They are described as symbioticbecause the fungus receives photosynthetically derived carbon compounds and the planthas increased access to mineral nutrients and sometimes water. The two most commonassociations are the arbuscular endomycorrhizas (AM) formed by Zygomycete fungi, andthe ectomycorrhizas (ECM) formed by Basidiomycetes, Ascomycetes, and a fewZygomycetes. Other mycorrhizal associations include the orchid, ericoid, arbutoid,monotropoid and ectendo- mycorrhizas (Brundrett et al., 1996).Mycorrhizal associations predominate in most natural terrestrial ecosystems(Brundrett, 1991). Whereas the AM fungi are widespread geographically and have a veryextensive host range, the ECM fungi are more restricted, forming associationspredominantly with genera of important woody plants. Nevertheless, ECM fungi aredominant components of the ground-dwelling macro-fungi in ecosystems where membersof the following plant families abound: Betulaceae, Dipterocarpaceae, Fagaceae,Myrtaceae, Pinaceae, Ulmaceae, Salicaceae. ECM fungi are common in tropical forests ofAsia but are uncommon in many forests in Africa and South America. In Asia, the numberof host species tends to increase with altitude and at higher latitudes.

ROLES IN ECOSYSTEMS:  

The ecology of mycorrhizal fungi is not well documented (Abbott and Gazey,1994; Francis and Read, 1995). Hence, in the discussion that follows, conclusions aremostly drawn from short-term studies with a small range of partnerships, often underexperimental conditions. In nature, the situation is far more complex as a single tree mayhave fungal partners which can vary in time and space. The study by Moyersoen et al.,(1998), on the co-occurrence of AM and ECM fungi in rainforest in Cameroon, provides a
good example of a field study exploring possible functional roles of mycorrhizal fungi.More studies of this type are needed to elucidate the dynamics of mycorrhizal fungi inecosystems and the impact of disturbance. Carbon transport The fungal/plant interface provides a conduit for the movement of carbon fromthe plant to the fungus, and for movement between plants linked by mycelia (Francis andRead, 1984; Simard et al., 1997; Wu et al., 2001). The nature of the interface and its modeof regulation are still being elucidated (Hall and Williams, 2000). It is generally believedthat mycorrhizal plants direct more of their photosynthates into the soil thannonmycorrhizal plants. This extra carbon accumulates in patches and at the edge of hyphalmats (Finlay and Read, 1986), and boosts the energy supply to the detrital food web,benefiting saprohytic microbes and other soil organisms (Barea, 2000). Because thechemical (Dieffenbach and Matzner, 2000) and physical environment around mycorrhizas(the mycorrhizosphere) differs from nonmycorrhizas, presumably it provides microhabitatsfor soil biota that are not present in the rhizospere of nonmycorrhizal roots. Mycorrhizal fungi are estimated to consume from 15 to 50% of net primaryproduction (Fogel and Hunt, 1979; Vogt et al., 1982). Nutrient cycling and nutrient conservation Fungi are crucial components of ecosystems as they transport, store, release andcycle nutrients. A good example of the potential of mycorrhizal fungi to capture anddeliver nutrients to their host comes from studies using inoculated eucalypts in field trialsin sub-tropical China. Generally, trees in this region grow well below their potential. Themain constraint to productivity appears to be low soil fertility (Dell and Malajczuk, 1994;Xu and Dell, 1998). Most of the land available for plantation forestry have been degradedover recent centuries with extensive loss of the A horizon caused by population pressure,inadequate management and over-harvesting (Xu, 1996). Topsoil crusting is common,contributing to enhanced erosion, reduced soil water storage, compaction and poor rootdevelopment (Xu et al., 2000). Low soil organic matter (SOM) content (<2%) alsorestrains productivity. As most soils for plantation eucalypts in southern China have losttheir Ao layer, we need urgently to consider how to recover microbial biodiversity as thereis no doubt that this will be important for improving long-term soil fertility. The capacityof some ECM fungi to promote both early growth and survival of eucalypts is veryimportant for commercial plantations on these disturbed and difficult sites. Significanteffects of ECM fungal inoculation on growth of plantation eucalypts were obtained at twosites in southern China (Xu et al., 2001). Effects were isolate dependent with someisolates stimulating tree growth and some isolates depressing tree growth. Similar resultswere obtained in a trial in the Philippines where two isolates increased survival while oneisolate decreased survival of Eucalyptus urophylla (Aggangan et al., 1999). Theimprovement in growth could be attributed to the acquisition of P as other essentialmineral nutrients were supplied at establishment. Generally, inoculation only increasedstand volume under P-limiting soil conditions. In forests, litter is an important nutrient reservoir. ECM fungi can mobilise P, N
and other nutrients from litter to tree roots (Attiwill and Adams, 1993; Perez-Moreno andRead, 2000). Fogel (1980) estimated that ECMs account for 43% of the annual turnoverof N in a Pseudotsuga menziesii forest in Oregon. Litter type can affect the diversity andfunction of ECMs (Conn and Dighton, 2000). Buscot et al., (2000) propose that the highdiversity of fungal partners that a tree may have allows optimal foraging and mobilisationof various N and P forms from organic soil layers. Soil structure It is obvious from the examination of ECM mycelial mats, that mycorrhizal fungihave a big impact on soil structure. Yet, there is scant information in the literatureregarding soils in tropical ecosystems. In agricultural soils, AM fungi increase theformation of soil aggregates (Bethlenfalvay et al., 1999). Food for animals Long-distance dispersal of spores from ECM fungi with hypogeal (truffle-like)sporocarps depends largely on mammal mycophagy (Kotter and Farentinos; Claridge andMay, 1994). Mycophagy is widespread and has been demonstrated in Europe, Australasiaand North America. Mycophagy serves to maintain populations of ECM fungi andprovides nourishment to small mammals (Malajczuk et al., 1987). Sporocarps are goodsources of water, protein, carbohydrates and minerals (Johnson, 1994; Claridge et al.,1999). The tripartite relationship between truffles/truffle-like fungi, vertebrates such assquirrels and many ground-dwelling marsupials, and the host trees, are well known. Lesswell known is the role that mycorrhizal fungi play as a food source for invertebrates andthe role of invertebrates in dispersal of ECM and AM fungal spores.

Q) Explain the key differences between bryophyte, gymnosperm, and angiosperm reproductive life-cycles.

Key Differences Between Angiosperms and Gymnosperms

Following are the substantial key differences between angiosperms and gymnosperms:

1. Angiosperms consist flowering ornamentals, fruits, and all vegetables and hence called as flowering plants, while gymnosperms contain all kind of pine, fir, pine, conifers, cedar, juniper, cypress and hence called as non-flowering plants.
2. Angiosperms contain sporophylls which get accumulated to produce flowers, angiosperms are generally bisexual and rarely unisexual, whereas gymnosperms also contain sporophylls which get accumulated to form cones.
3. Structural differences
   • Sepals and petals present in angiosperms, which are not been possessed by gymnosperms.
   • Sporophyll bears short thalamus in angiosperms; it (sporophyll) bears elongated central axis gymnosperms.
   • Megasporophyll is structured to form a carpel as well, microsporophyll is represented by a stamen, consisting of stamen and filament in angiosperms, whereas gymnosperms have a woody part and microsporophyll is represented by a broad, sterile head. No distinction in anther and filament.
   • In angiosperms stigma and style are present and usually, four microsporangia or pollen sacs are present. In gymnosperms stigma and style are absent and microsporangia vary from two (Pinus) to several hundred in Cycas.
   • Ovules are present inside the ovary part of the carpel; these are attached to the placenta, these (ovules) are produced on a stalk or funiculus in angiosperms. While in gymnosperms ovules lie on the megasporophyll and are not borne on the placenta and they (ovules) are sessile.
   • An ovule is covered by few thin integuments of slender micropyle in angiosperms; whereas in gymnosperms an ovule is covered by three layers of integuments of wide micropyle.
   • Angiosperms, the female gametophyte contains seven-celled and eight nucleate embryo sac whereas in gymnosperms the female gametophyte is parenchymatous and large.
   • Archegonia are absent and Tube cell and a generative cell is present in male gametophyte, which divides and form two male gametes in angiosperms; Distinct archegonia are present and one or two prothalial cell, stalk cell, tube cell and a body cell, which further divides into two male gametes in gymnosperms.
   • In angiosperms, embryo contains one or two cotyledons and the seeds develop inside the ovary part of the carpel which matures into a fruit. In gymnosperms embryo contains one or many cotyledons, even the seeds develop on the megasporophyll and fruits are never formed.
   • Double fertilization process is there, where both the male gametes are in active state and one play the role for generative fertilization and other for vegetative fertilization or triple fusion in angiosperms; while in gymnosperms there is only one generative type of fertilization and only one gamete is functional.

Angiosperms are also the source of the world’s hardwoods. Flowering plants are economically important as they serve as a source of pharmaceuticals, timber, ornamentals, fiber products, and other commercial uses, whereas gymnosperms are known for providing softwoods such as pine, fir and use to make paper, lumber, and plywood.

The defining features of bryophytes are:

• Their life cycles are dominated by the gametophyte stage
• Their sporophytes are unbranched
• They do not have a true vascular tissue containing lignin (although some have specialized tissues for the transport of water)